Ecological Research Series
EFFECT OF AIR POLLUTION ON
Pinus strobus L. AND GENETIC
RESISTANCE
A Literature Review
I
55
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$33
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Environmental Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Corvallis, Oregon 97330
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application of
environmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The five series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal
species, and materials. Problems are assessed for their long- and short-term
influences. Investigations include formation, transport, and pathway studies to
determine the fate of pollutants and their effects. This work provides the technical
basis for setting standards to minimize undesirable changes in living organisms
in the aquatic, terrestrial, and atmospheric environments.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/3-77-002
January 1977
EFFECT OF AIR POLLUTION ON PINUS STROBUS L.
AND GENETIC RESISTANCE
A Literature Review
by
Henry D. Gerhold
The Pennsylvania State University
University Park, Pennsylvania 16802
Contract No. P5J10504-J
Project Officer
Raymond G. Wilhour
Terrestrial Ecology Branch
Ecological Effects Research Division
Corvallis Environmental Research Laboratory
Corvallis, Oregon 97330
CORVALLIS ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U. S. ENVIRONMENTAL PROTECTION AGENCY
CORVALLIS, OREGON 97330
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DISCLAIMER
This report has been reviewed by the Corvallis Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily
reflect the views and policies of the U.S. Environmental Protection
Agency, nor does mention of trade names or commercial products consti-
tute endorsement or recommendation for use.
n
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FOREWORD
Effective regulatory and enforcement actions by the Environmental
Protection Agency would be virtually impossible without sound
scientific data on pollutants and their impact on environmental
stability and human health. Responsibility for building this data
base has been assigned to EPA's Office of Research and Development
and its 15 major field
Environmental Research
installations, one
Laboratory (CERL).
of which is the Corvallis
The primary mission of the Corvallis Laboratory is research on the
effects of environmental pollutants on terrestrial, freshwater, and
marine ecosystems; the behavior, effects and control of pollutants
in lake systems; and the development of predictive models on the
movement of pollutants in the biosphere.
This report summarizes knowledge which may be used in providing
protection to white pine, a valuable timber and ornamental tree
species.
A.F. Bartsch
Director, CERL
m
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ABSTRACT
Effects of the main phytotoxic gases that injure eastern white pine
(Pinus strobus L.) and the possibilities of breeding resistant trees are
discussed in a comprehensive literature review. The main purpose of the
report is to summarize knowledge which may be used in providing protection
to a valuable species. Implicitly related topics are reviewed briefly,
including sorption and emission of gases by plants, air quality standards,
bioindicators for monitoring air quality, and silvicultural measures for
protecting trees against injuries. Extensive studies in growth chambers
and in nature indicate that widespread and in places very serious damage
has been caused by ozone, sulfur dioxide, and nitrogen oxides. There
is good reason to be concerned about not only acute injuries, but also
chronic effects that probably reduce the growth of this species and
other trees. Air pollutants may also disrupt forest ecosystems less
perceptibly, though over vast areas. A large body of existing knowledge
apparently has been utilized very little for protecting trees exposed to
this hazard. It appears doubtful that current emission abatement efforts
will improve air quality enough to adequately protect the more sensitive
species and individuals. Recommendations are made for shifting research
emphasis toward developing and implementing strategies that will provide
greater protection in forest ecosystems and among landscape trees.
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CONTENTS
Page
Abstract iv
SECTIONS
I. Introduction 1
Perspectives on the Problem 1
Purpose of the Report 2
II. Conclusions 7
III. Recommendations 9
IV. Air Pollutant Effects on Eastern White Pine 10
Nitrogen Oxides 11
Ozone 12
Sulfur Dioxide 14
Mixtures of Ozone, Sulfur Dioxide, Nitrogen Oxides 16
V. Breeding Trees for Improved Resistance to Air Pollution 20
Genetic Variation in Resistance 21
Selection Methods 24
Inheritance of Resistance 26
Breeding and Propagating Methods 27
VI. References 30
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SECTION I
INTRODUCTION
PERSPECTIVES ON THE PROBLEM
Eastern white pine, Pinus strobus L.. probably is injured by air
pollutants more than any other tree species in eastern North America. It
certainly is one of the most sensitive. Estimates of damage to trees
and economic values have been made for only a few cases of the most
obvious or extensive injuries. Among the best known examples is the
elimination of the species from large areas in Ontario, Canada, by fumes
from smelters (Gordon and Gorham 1963, Gorham and Gordon 1960). Damage
in several localities has occurred on thousands of acres and losses may
involve millions of dollars. An aerial survey of two counties in North
Carolina showed that white pine foliage was injured in an area estimated
to be 112,640 acres, with 100 trees affected per square mile (Landgraf
et_ aj_. 1969). Many large trees lost all their needles and died, some of
them in residential areas where they had high aesthetic values; insect
attacks on weakened trees posed a continuing threat. Ten percent of the
white pines throughout Pennsylvania were estimated to have been injured
by one air pollution episode in 1972 (Nichols 1972). In a 1966 survey
of white pine plantations in Wisconsin, needle blight symptoms were
found in almost every plantation (Prey 1968). An out-of-court settle-
ment of $450,000 was paid to Christmas tree growers for alleged damage
caused by air pollutants from a power generating station. It represents
about one-fourth of the claimed damage to 500,000 trees of several
species, including white pine (Edwards 1972). Litigation has been
brought in additional cases. Other examples of injuries are cited
elsewhere in this report, and experts are aware of many others which
have not been recorded. The true extent of this damage cannot be esti-
mated accurately from available data, but it must be extremely large.
The damage caused by air pollutants to eastern white pine is only a
small part of a global problem, affecting countless individual trees and
entire forest ecosystems. The literature contains numerous published
accounts of air pollutant injuries, either proven or probable, to sensi-
tive trees in various industrial regions of several continents. Some of
the best substantiated cases have been described in various literature
reviews (Hansbrough 1967, Hepting 1964, Hepting 1968, Horntvedt 1970,
Keller 1968, Kisser 1966, Knabe 1966, Knabe 1972, Materna 1969, Wentzel
1967). One of the earliest reports of damage to forests by industrial
fumes in the United States appeared some 50 years ago (Tourney 1921).
Scientists have been cognizant of the phytotoxic effects of industrial
fumes for more than 100 years (Grouven 1855, Sttickhardt 1871), but a
preponderance of the research on the subject has been conducted during
the past 20 or even 10 years.
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The cause of a recently discovered hazard to forests, termed "acid
rain", also may be traceable to air pollutants. In both North America
(Likens e_t aj_. 1972) and Europe (Oden 1968), a trend of increasingly
acidic rainfall has been linked to sulfur and nitrogen oxides given off
when fossil fuels are burned. Potentially serious effects on forest
ecosystems are anticipated, though some experts have expressed dissent-
ing views. Forest measurements in Sweden do indicate that a decline in
forest productivity has occurred (Jonsson and Sundberg, 1972). Small
reductions may be involved, but over vast areas, so that economic losses
could be very great.
When dramatic or less obvious effects of air pollutants on eastern
white pine are under consideration, one should be aware also of possible
side effects. The species occurs not in isolation but as a member of an
ecosystem. Ulrich (1972) has outlined relationships of air pollutants
with forest ecosystems which may cause disturbances in a steady state.
The situation in temperate regions has been reviewed by Smith (1974). He
classified relationships ranging from vegetation functioning as a sink
for pollutants, to subtle or severe effects which can cause various
kinds of stresses or mortality. These in turn may have varying impacts
on ecosystems.
In reviewing interactions between air pollutants and plant para-
sites, Heagle (1973) found indications that pollution stress may decrease
obligate parasitism but increase facultative parasitism. For example,
infection by Cronartium ribicola on white pine was less severe close to
a smelter that emitted SO-; white pine weevil incidence was higher on
trees injured by SCL, but the insects caused less damage. Plant reac-
tions are highly dependent on environmental conditions and on genetic
characteristics. Data on the latter are quite limited, and less well
understood, especially in nature.
PURPOSE OF THE REPORT
It has been shown that eastern white pine, a species having con-
siderable commercial and ornamental importance, has been damaged exten-
sively by air pollutants. The general purpose of reviewing research,
results, therefore, is to summarize existing knowledge so it may be used
in providing protection to this valuable tree. What has been learned
about eastern white pine might apply also to other species which have
received less attention. Furthermore, gaps in knowledge may be identi-
fied to indicate further research needs.
There are different ways of providing protection, and these re-
quire various kinds of information. The main body of the report is
organized according to the two main topics: effects of specific air
pollutants and the methodology of producing resistant varieties. How-
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ever, the information contained therein may be applied also to the
following subjects, which are considered to be implicitly related to the
purpose of this report.
1. sorption of pollutants by plants
2. emission of gases from plants
3. air quality standards for pollution abatement
4. bioindicators for monitoring air quality
5. silvicultural measures for protecting against injuries
6. uses of trees for improving human environments
These topics are discussed briefly here to amplify how they are related
to the overall purpose.
The sorption of pollutants by trees (Roberts 1971) is of interest
in understanding how injuries occur, and also in defining the ability of
vegetation to improve air quality. Experiments in specially designed
chambers with alfalfa (Bennett and Hill 1973, Hill 1971) indicated that
vegetation may be effective in removing large quantities of pollutants
from the air. HF, SCL, and NO^ were removed efficiently; 0- was readily
deposited on surface tissues; very little NO or CO absorption was detected
Uptake rates increased linearly with concentration, and were influenced
also by wind velocity, light intensity, and depth of the leafy canopy.
Waggoner (1971) described a method for calculating uptake rates based on
resistances of leaves to gas exchange, and for transfer in the atmosphere
based on meteorological conditions. Ozone sorption studies (Hanson and
Thome 1970, Thorne and Hanson 1972) showed that rates of herbaceous
species were four to seven times as great as those of woody species of
Quercus, Ginkgo, Camellia, and Bougalnvillea. They were higher for
actively growing tissues than dormant tissues. A strong positive corre-
lation was found between sorption rate and transpirational water loss.
In some species uptake fell off as fumigations continued. Variation in
concentrations of 0.17 to 1.04 ppm 0., had little effect on sorption_
rates. In another series of ozone experiments (Townsend 1974), deciduous
tree species differed significantly in uptake rates at concentrations of
0.2 to 0.8 ppm. White oak and white birch leaves removed the largest
quantities, while red maple and white ash were the least efficient.
Uptake by white birch was linear over the range 0.1 to 0.8 ppm, and
decreased very little during eight hours of exposure. Uptake by red
maple populations differed significantly. Similar studies with sulfur
dioxide (Roberts 1974) also revealed large species differences. Sorp-
tion rates of red maple, white birch, and sweetgum (0.26 to 0.27 mg
S07 - h~ . g~ ) were much greater than rhododendron and azalea (0.07 to
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0.08), while firethorn, privet, and white ash were intermediate. The
capacity to remove S0? was influenced little by a range of concentra-
tions from 0.2 to 1.0 ppm or by exposure periods of one to six hours.
The contribution of trees toward improving air quality is still a
controversial subject despite the convincing and compatible results of
several carefully controlled experiments. Mooi (1974) concluded that
the amounts of hydrogen fluoride removed by trees during long exposures
contributes little to air purification; uptake rates were estimated from
fluorine contents of leaves. Extensive measurements by Lampadius (1966,
1968) within and outside forests did not support the expected filtering
capability. He concluded that forests have little if any effect in
lowering S0? concentrations. The data were quite variable, and seemed
to be influenced mainly by exchange of air masses. Though the author
did not mention it, the possibility remains that a more careful analysis
of turbulence effects and gradients in vertical and horizontal directions
may be required to detect beneficial effects of trees. Brunig (1971)
believes that oxygen emissions from forests are too small to effectively
improve man's environment, but that increased turbulence caused by
aerodynamic roughness may cause pollutants to be diffused rapidly. He
regards increased air mixing as one of the most important nonproductive
functions of forests, besides providing recreational locales, local
noise abatement, dust absorption, and protection of soil and water
quality. Additional literature on this subject has been reviewed by
Keller (1971).
Little is known about the effect on humans of many substances given
off by plants. Vigorov (1966) has discussed possible beneficial or
detrimental influences. Rasmussen (1972) estimated that plant species,
including Pinus strobus, release six times as much volatile organic
substances as come from manmade sources. The fate of these gaseous
hydrocarbons in the atmosphere is unknown.
The relationship of air quality standards to pollutant injuries to
forests has been discussed by Knabe (1971). He pointed out that emission
standards in Germany permit slight to severe injuries to several tree
species, principally the most important timber species, Norway spruce
and Scotch pine. It has long been recognized that the most desirabje
way of alleviating such damage is by controlling pollutants at their
sources (Wentzel 1967). This has not proven to be a feasible solution,
however, for technical, economic, and social-political reasons. The
possibility of controls at emission sources that would be adequate for
protecting sensitive trees was considered remote, so other alternatives
for providing protection are being pursued. Heggestad (1969) reviewed
air quality standards for vegetation with respect to ozone. He con-
cluded that a total oxidant level of 0.15 ppm for one hour, which had
been selected as a standard for ambient air quality, will not be adequate
to protect sensitive vegetation in eastern United States. Ozone is re-
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garded as the most damaging of all air pollutants affecting vegetation.
More adequate air quality criteria for oxidants are urgently needed, and
more background information is required for the setting of standards.
The use of sensitive plants as bioindicators to monitor air pollu-
tants has been explored by Berry (1964, 1973). Eastern white pine
clones were selected that will detect low levels of oxidants, sulfur
dioxide, or fluorides. Pollutants may be identified by using clones
that are sensitive to only one type. Out of 1428 seedlings that sur-
vived from an original population, 53 were sensitive only to oxidants, 8
to sulfur dioxide, and 14 to fluorides. Only 64 (4.5%) were tolerant to
all three types of pollutant regimes to which they were exposed. The
feasibility of selecting and propagating sensitive clones has been
clearly demonstrated. Plant indicators have several advantages over
instruments, the chief of which may be low costs and automatic integra-
tion of all pollutant and environmental variables which influence in-
juries to vegetation. There may be operational difficulties in estab-
lishing a bioindicator network, as Baer (1967) reported. However, systems
using several kinds of plants have been operating successfully in Germany
(Guderian and Stratmann 1968, Schtinbeck e^ al_. 1970).
The adoption and implementation of air quality standards, monitor-
ing systems and enforcement procedures probably will not provide adequate
protection to all forest and landscape trees. Wood (1968) predicted,
even bevore the onset of current energy problems, that the most damaging
phytotoxic air pollutants would worsen until 2000 A.D. despite abatement
procedures, and that serious problems would remain for some time after-
wards. SiIvicultural measures which may be taken to protect forests
against air pollutants have been reviewed by Keller (1964, 1968) and
Kisser (1966). These include principally site improvement (e.g., fertilizing),
changing species by selection during natural or artificial regeneration,
and breeding more resistant varieties. Existing knowledge is inadequate,
in many respects, for implementing such measures.
In justifying the protection of trees against air pollutants, it
should be recognized that their usefulness goes beyond the commercial
products derived from them. Baumgartner (1971) discussed the importance
of forests to the biosphere in regard to air pollution uptake, noise
absorption, and energy exchange. Urban planners are interested in trees
not only for their beauty, but also for their capacity to influence
noise, air pollution, microclimate, and the water supply (Smith 1970).
The most important contribution in ameliorating urban microclimates is
the interception of solar radiation by trees on hot summer days (Heisler
1974). Cooling by transpiration could be important, but little is known
about availability of water which is needed if trees are to function as
nature's air conditioners. Human comfort may be improved by a lowering
of wind speeds in the winter, but summer breezes may also be reduced.
Trees can play a significant role in noise control in suburban and rural
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areas, especially when used in combination with land forms and struc-
tures (Herrington 1974). A belt of trees can reduce noise by three to
eight decibels per 100 feet of depth, depending on its density (Reethof
1973). A 200 foot wide belt would be required to reduce noise from a
heavily travelled highway, to acceptable levels in a residential area on
the other side of the noise barrier. Bernatzky (1968) discussed the
design of urban tree plantings for maximum effectiveness in filtering
out gaseous and particulate pollutants, improving microclimate, and
reducing noise. Plans have been formulated for using German forests for
air cleansing, noise abatement, and related functions (Knabe 1973).
Research needs related to the purpose of this report have been
identified by several authors, for various geographic regions or subject
matter areas. Air pollutants are recognized as an important part of the
problem of growing trees for the 45 million people in Megalopolis
(Doolittle 1969). Information is needed in relation to choosing species
for planting and breeding pollution resistant varieties. Heck et al.
(1973) and Hansbrough (1967) discussed relationships between forest or
ornamental trees and air quality, pointing out numerous gaps in our
knowledge. Knabe (1966, 1967) provided European insight into air pollu-
tion research needs of the United States. He regarded Pinus strobus a
promising species for resistance breeding, because it shows great varia-
tion in resistance and can be propagated vegetatively. A more recent
literature review (Knabe 1972) is particularly useful, even though it
emphasizes mainly Germany's research needs. These are classified accord-
ing to their value in meeting practical applications, or their potential
for leading to new methods for the solution of problems. Subjects
covered include regional distribution of damage, diagnosis, evaluating
losses, methods for reducing damage, defining boundaries of emission
areas, setting air quality criteria and risks, biological indicators,
physiological mechanisms, and secondary effects. Kisser (1966) has
discussed air pollution research needs from the view point of biological
knowledge, as this relates to injuries and land management problems.
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SECTION II
CONCLUSIONS
Eastern white pine has been damaged substantially by phytotoxic
gases in many places. Air pollution is likely to pose a hazard to this
species and others for a long time. Sulfur dioxide, ozone, and nitrogen
oxides are regarded as the most important pollutants that damage this
species. Direct effects of ozone and sulfur dioxides have been studied
extensively in fumigation experiments and in nature, and there is some
effects information on effects of nitrogen oxides and gas mixtures.
Less is known about chronic effects and very little about indirect
influences on ecosystems, though scientists have expressed concern about
these problems.
Nitrogen oxides can injure foliage and reduce height and diameter
growth of white pines, which vary greatly in sensitivity. Nitrogen
oxides, alone or mixed with sulfur dioxide, inflict damage resembling
the chlorotic dwarf disease caused by ozone and sulfur dioxide.
Ozone injuries to pine needles have been described in great detail,
and the dosages and environmental conditions which are conducive to in-
juries are understood quite well. There have been a few studies on
physiological effects and relationships with fungi. While white pine is
generally quite sensitive to ozone and also sulfur dioxide, some clones
are much more vulnerable than others.
Sulfur dioxide from industrial emissions has caused severe and
extensive damage to white pines. Knowledge about threshold concentra-
tions of sulfur dioxide and environmental influences on injuries comes
mainly from outdoor studies and some fumigation experiments. Fertilizer
applications have reduced injuries in several instances.
The mixtures of gases to which trees may be exposed in nature make
it difficult to diagnose injuries, and almost impossible to prove the
cause with complete certainty. Clear, ample evidence does exist that
the rather common chlorotic dwarf disease of white pine is caused by
ozone and sulfur dioxide, and these gases are responsible for the vari-
ously named symptoms associated with it. Semi-mature needle blight, a
similar physiogenic disease, is different in certain respects.
Breeding varieties with improved resistance to air pollutants can
be justified as a component of a pollution control strategy, not as an
alternative to controlling emissions. Improvement objectives include
resistance to major pollutants at concentrations below those injurious
to humans, environmental adaptation, resistance to other pathogens, and
other qualities related to uses of trees for timber or amenity purposes.
Specific goals need to be clearly defined. Evidence of wide genetic
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variation found in at least 15 tree species, including eastern white
pine, indicates ample opportunities for selection. Populations from
regions with harsher climates seem to have higher levels of resistance.
These might have pre-adapted tolerance to air pollutants because of
their ability to withstand adverse natural conditions such as droughts
and frosts. Selection methods that have been used successfully include
phenotypic selection in damaged forests, fumigation of young trees in
chambers of various types, and pre-selection using rapid tests of cut
branches or leaves. Environmental variables and data frequency distri-
butions have received attention in designing selection procedures and
making genetic estimates. Clonal repeatability analyses and heritability
estimates indicate moderate to strong genetic control over resistance to
air pollutants in white pine and Scotch pine. Breeding projects to
improve resistance to air pollutants have been started for Norway spruce,
Scotch pine, European and Japanese larches, poplars, red maple, and
white pine. Various methods have been employed, and initial progress
has been encouraging. Some very important research problems have been
identified which will require long-term support for reducing air pollu-
tion damage to timber and landscape trees species.
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SECTION III
RECOMMENDATIONS
Emphasis in research should shift now from extending knowledge
about pathological effects of air pollutants toward protecting eastern
white pine and other tree species against excessive damage. Reasonable
goals should be defined, a strategy developed, a set of plans imple-
mented, and supporting research continued.
Goals for protecting trees against air pollutants surely will
represent a compromise. Increased costs of emission abatement or of
breeding resistant cultivars should be balanced against additional
protection attained. Both tangible and intangible values of reducing
visible injuries and restoring better growth rates should be considered.
The development of a strategy and the plans to implement it will
require additional information. Surveys of damage to forests and land-
scape trees will be needed to subdivide geographic regions according to
risk classes. Existing eastern white pines or planted bioindicator
clones can serve as standards for comparisons. Localities characterized
by the most favorable benefit/cost ratios should receive attention
first, and others proportionately.
A carefully integrated, dynamic research program should be developed
to support protection efforts. Frequent reviews of technical aspects
and comparisons of costs to benefits are advisable. Research areas
which deserve high priority include short- and long-term impacts of air
pollutants on forest ecosystems and landscape trees; pathological effects
of gas mixtures; genetic variation in sensitivity of natural populations;
and breeding of resistant cultivars.
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SECTION IV
AIR POLLUTANT EFFECTS ON EASTERN WHITE PINE
Air pollutants conceivably might have some favorable effects on
eastern white pine, but most of the pertinent literature is concerned
with direct injuries to individual trees and forests. The immediate
impact and the ultimate significance of such injuries for individuals
and for ecosystems is not obvious in many cases. A classification of
the kinds of effects proposed by Smith (1974) offers a useful frame of
reference. Class I effects occur at low dosages, during which vegeta-
tion is uninjured and may act as an important sink for contaminants.
Class II effects at intermediate dosages may adversely affect sensitive
individuals or species by nutrient stress, reduced photosynthesis or
reproduction, predisposition to insects or microbes, or direct disease
induction. Class III effects at high dosages may induce acute morbidity
or mortality. Deleterious consequences may include reduced forest
productivity, shifts in species composition, and disease or insect
outbreaks. In some instances, nutrient cycling, water yield and quality,
microclimate, soil erosion tendencies, and overall stability in an
ecosystem can be affected adversely.
Conifers are among the plants most sensitive to air pollutants, be-
cause of the long life of their assimilation organs and the low capability
for regeneration. Halbwachs (1971) has summarized chronic and acute in-
juries to conifers caused by several pollutants to foliage and entire
plants. Microscopic effects on needle tissues and physiological reactions
also are described. Typical symptoms have been defined but these often
resemble symptoms resulting from other stresses. This has caused continu-
ing difficulties in investigations, and is one of the reasons why fumiga-
tion chambers have been used widely for qualitative and quantitative
control of exposure.
The terminology applied to diseases of eastern white pine caused by
air pollutants has caused some confusion (see Costonis and Sinclair 1969
a, b, Houston 1974). "Needle blight" is a general term which has been
used for a group of symptoms; these may include dwarfing, chlorotic or
necrotic tissues, and banding. It originated before air pollutants "had
been proven to be causal agents. "Chlorotic dwarf" also refers to a
syndrome of leaf symptoms, leading to stunting of whole plants, probably
caused by mixtures of ozone and sulfur dioxide (Dochinger et^ aj_. 1970,
Dochinger and Heck 1969, Dochinger and Seliskar 1970), and possibly also
by oxides of nitrogen and sulfur dioxide (Skelly e^ al_. 1972). The
phenological stage when portions of needles are most sensitive is a
principal basis for distinguishing between "emergence tipburn" (Berry
and Ripperton 1963), "post emergence chronic tipburn" (Berry and Hepting
1964), and "semimature tissue needle blight" (Linzon 1967). The names of
other white pine needle disorders (Costonis and Sinclair 1969 a) are
not common in recent literature: "yellow dwarf", "red needle blight",
10
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"short needle". Many articles do not refer to a disorder by name, but
rather describe symptoms caused by specified pollutants.
The protocol in this report is to discuss effects that are attribut-
able to the pollutants nitrogen oxides, ozone, sulfur dioxide, and
mixtures of gases. Relationships to the principal named diseases are
discussed in conformance to terminology in the literature.
NITROGEN OXIDES
Published information on nitrogen oxide effects on eastern white
pine is not very extensive. Several pines were examined for injuries in
Virginia near a source of moderately high concentrations of NO and NOp
(Skelly et al. 1970). Ambient levels were monitored at seven stations,
and the highest one hour concentration was over 0.58 ppm at a distance
of 0.5 mile from the source. Levels of S02 at the same station were
0.67 ppm for a two hour collection period at the same period. At one
mile or more from the source, native Pinus strobus had developed signi-
ficant chlorotic mottle on older needles and some tipburn. Some highly
sensitive trees had severe chlorosis and reduced height growth. Pinus
strobus seedlings, planted 200 yards from the source three years prior
to the study, were severely stunted, showed no appreciable growth after
planting, and had tipburn. Pinus taeda, P. echinata and P. virginiana
apparently were less susceptible. They also had chlorotic mottle and in
some instances severe chlorosis and tipburn, but no significant growth
losses. Striking tree to tree variation in sensitivity existed in Pinus
strobus (Skelly et_ aj_. 1972). It was concluded that oxides of nitrogen
at moderate concentrations, acting alone or with low sulfur dioxide
concentrations, may cause acute or chronic damage to conifers. The
damage to white pines appears similar to chlorotic dwarf disease caused
by ozone and sulfur dioxide.
Fluctuating operations of a munitions factory made it possible to
study effects of NO and N0? on diameter growth of Pinus strobus and
Liriodendron tulipifera (Stone and Skelly 1973, 1974). Production
levels of nitric acid and nitrated products were high during three
periods, and near zero during intervals between. Diameter growth was
measured on increment cores from natural stands within 0.2 mile of the
source. In both species growth was depressed 50 percent, but recovered
sharply during 1946-1949 when emissions were reduced. Significant
negative relationships were found between tree growth and munition
production levels (r =.50 and .52), and positive correlations were found
with rainfall (r =.37 and .43).
OZONE
The oxidants ozone, peroxyacetyl-nitrate, and nitrogen dioxide have
comparable but not identical effects on plants (Taylor 1968). Pinus
strobus is included among the most sensitive plants.
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Ozone was identified as a likely cause of emergence tipburn of
Pinus strobus quite recently (Berry 1961). Isolations of fungi from
roots did not reveal any causal pathogen. Injured trees recovered when
they were transplanted to areas where the severity of disease was lower.
Grafted scions retained their original condition regardless of rootstock
type. This evidence indicated that an atmospheric agent was responsible.
Ozone fumigation with 10 pphm for two hours caused typical symptoms on
ramets from one susceptible tree, and no symptoms on ramets from a
resistant tree. Ozone concentrations approaching 5 pphm can cause
emergence tipburn symptoms of white pine blight (Berry and Ripperton
1963). Very similar results were obtained when symptoms and concentra-
tions were monitored in field experiments and greenhouse fumigation
chambers. Potted, sensitive ramets were protected from injury in carbon
filtered chambers. Typical foliar symptoms are common on white pines in
urban locations, too (Hibben 1969).
The symptomatology of ozone injury to eastern white pine has been
described in detail (Costonis and Sinclair 1969, Sinclair and Costonis
1967). The blighted condition is a syndrome of acute and chronic ozone
injuries. The reactions of individuals vary greatly. A small proportion
of trees in a population exhibit mild symptoms each year and severe
injuries occasionally. A very small percentage is severely injured
every year. These are stunted and have conspicuously burned or chlorotic
foliage that is retained only one year instead of the normal 27 months.
The most tolerant trees have dark green foliage retained until September
or October of its third season. Needles of sensitive trees are suscepti-
ble to ozone injury from emergence until they have completed elongation
and hardened off. Acute injuries may occur on elongating needles after
experimental exposures to as little as 3 pphm for 48 hours or 7 pphm for
4 hours. The period of greatest susceptibility is in June and July.
The most sensitive tissue is in a zone a few millimeters wide located 10
to 20 mm from the needle sheath. If trees are injured several times,
the most recent injury occurs nearest the needle base. The first exter-
nal symptom is inconspicuous silver flecking visible only under magnifica-
tion. Flecks radiate from stomata in the sensitive zone, and are caused
by the collapse of mesophyll cells adjacent to stomata. Usually all
needles in a fascicle and most fascicles on a branch develop new symptoms
in the same portions of needles at the same time. After severe injuries
yellowish to pinkish spots develop which may become necrotic, and enlarge
to form shrunken dead bands, causing death of the needle tip which is
called "tipburn". The degree of injury to sensitive trees depends on
ozone concentration and environmental conditions. In the presence of
free moisture, "water spot" lesions may develop on any face of a needle,
instead of being restricted to stomatal surfaces; these are less depen-
dent on the stage of tissue maturity. Injuries are more likely to occur
at higher temperatures during and after fumigation and in the presence
of sunlight. Exposure to 40 to 60 pphm ozone caused symptoms different
from those found in the field or after fumigation with low concentrations,
and caused injuries to both susceptible and resistant trees (Costonis
and Sinclair 1969 b).
12
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The threshold of ozone dosage at which visible injuries to Pinus
strobus occur has differed greatly in various experiments. The lowest
dosages are 3 to 10 pphm for 1 to 48 hours (Berry 1961, Berry and
Ripperton 1963, Costonis and Sinclair 1969 a, b). Moderate dosages are
10 to 25 pphm for 4 to 8 hours (Berry 1971, Davis and Wood 1968, Davis
and Wood 1972, Wood and Davis 1969). A much higher threshold of 50 to
100 pphm for 4 hours has been reported by Botkin et_ at_. (1971, 1972).
Houston (1974) found that among 47 trees selected for sensitivity to
tipburn, none were injured when ramets were fumigated with 5 pphm for 6
hours; 20% were injured at 10 pphm; 60% at 30 pphm, and 20% at 60 pphm.
Genetic or environmental differences can explain the variation ob-
served in threshold dosages, and furthermore these are subject to sea-
sonal variation. This is supported by observations in several reports
already cited. In addition, a study of Pinus virginiana (Davis 1970)
may apply also to other pines. Ozone sensitivity was influenced by
environmental conditions before, during, and after fumigation. High
temperature before and after exposure increased sensitivity, but lowered
it during fumigation. High humidity during fumigation greatly increased
sensitivity, but had little effect before or afterwards. Age of seed-
lings does not appear to be an important source of variation, as three,
five, and seven week old pines did not differ in sensitivity, and they
behaved much like two to five year old trees (Berry 1971).
Ozone can also influence physiological processes below threshold
exposures, without any visible symptoms developing other than reductions
in growth. Photosynthesis was depressed and respiration was stimulated
in young seedlings of Pinus strobus and three southern pines exposed to
5 to 15 pphm 0, for 5 to 18 weeks (Barnes 1972a). In contrast, Botkin
et^ aj_. (1971) Had to use dosages of 50 to 100 pphm for 3 to 7 hours to
demonstrate supression of photosynthesis. Total soluble carbohydrates,
reducing sugars, and ascorbic acid were elevated after prolonged expo-
sures to 5 pphm (Barnes 1972b). In seedlings exposed to 15 pphm, soluble
sugars were higher than in controls, but ascorbic acid was not. Carbohy-
drate and ascorbic acid levels may be useful in estimating needle matur-
ity and sensitivity to ozone (Barnes and Berry 1969). Effects of ozone
on C0? fixation patterns were studied using Pinus strobus seedlings and
detacned shoots (Wilkinson and Barnes 1973). Dosages as low at 10 pphm
for 10 minutes caused significant differences. Results indicate the im-
pairment of enzymes involved in the transfer of carbon into sucrose. An
increase of C in alanine was the most consistent effect, and may be
one of the earliest detectable manifestations of ozone effects at the
biochemical level.
Relationships of Pinus strobus with fungi may be influenced by
ozone (Costonis and Sinclair 1967, 1972). Lophodermium pinastri and
Aureobasidium pullulans were isolated most frequently from injured needles,
13
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the latter only from dead tissues. L_. pinastri was isolated more fre-
quently from trees susceptible to ozone than from resistant ones, whether
or not they had been fumigated.
The relative sensitivity of Pinus strobus to ozone has been com-
pared to other species by several investigators. Davis and Wood (1972)
found that several conifers and hardwoods were more sensitive, others
more resistant. Such comparisons are subject to the kinds of variation
discussed in relation to thresholds. Whether the criterion is leaf in-
jury or impact on the growth and health of whole plants can also make
quite a difference. No matter how available data are interpreted, how-
ever, Pinus strobus is rather sensitive to ozone.
SULFUR DIOXIDE
Industrial emissions of sulfur dioxide have caused extensive damage
to white pines. Concentrated fumes near metal smelters have eradicated
the species within five miles, caused mortality and severe injuries at
distances of at least 20 miles, and other effects have been traced to 30
miles (Gordon and Gorham 1963, Gorham and Gordon 1960). In a 720
square mile area where the most severe injuries occurred near Sudbury,
Canada, direct damage to trees in a 10 year period was estimated at
$117,000 (Linzon 1971, 1973), though only 7.6 percent of the trees in
productive forests were white pines.
Sulfur dioxide concentrations and injuries to vegetation around
Sudbury have been reported for the period 1964-1968 (Dreisinger and
McGovern 1970). Half-hour concentrations reached 286 pphm, compared to
364 pphm during the previous 10 year period. At ten stations the pres-
ence of sulfur dioxide was recorded 13% of the time. Concentrations
were above 25 pphm 1.26% of the time, and above 50 pphm 0.38% of the
time. Dosages considered to be injurious to vegetation were 95 pphm for
one hour, 55 pphm for two hours, 35 pphm for four hours, or 25 pphm for
eight hours. Because environmental conditions modify plant responses,
injuries have failed to occur in some instances at concentrations two to
four times greater. In other cases, injuries have occurred at levels 25
percent less than these concentrations, and always during June or July
when hot, humid weather prevailed. Over 2000 square miles were subjected
to one or more potentially injurious fumigations during the five year
period, and 1,271 square miles to five or more. Trembling aspen, jack
pine, white birch, and white pine were the most sensitive trees when
ranked according to foliage injuries. White pine suffered most from
repeated heavy fumigations, however, while the aspen and birch recovered
more readily. The most resistant species were red oak, sugar maple,
white spruce, and cedar.
14
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Severe injuries have also been attributed to emissions of sulfur
dioxide from petroleum refineries (Linzon 1965) and coal burning power
generating stations (Drummond and Wood 1967, Gordon 1972). In addition
direct injuries to foliage, effects on seeds may also inhibit natural
reproduction, at least in Scotch pine (Mrkva 1969). Pines exposed to
higher concentrations of sulfur dioxide produced smaller cones, less
seed, and lighter seed than those farther from the source of emission.
Chemical analyses of plant tissues have given us some insight into
injuries caused by sulfur dioxide. Bortitz (1968) demonstrated that
sulfur dioxide is taken up by conifers not only during the growing
season, but also in the winter; it can be translocated on warm winter
days and is capable of damaging plants. Sulfur contents of foliage can
confirm exposure to SCL, and thus is useful in diagnosing injuries
(Stefan 1971). Branches of Pinus strobus and four other pines were
fumigated with SCL to study uptake and contents under various conditions
(Godzik 1972). Accumulations were greatest in the tips of needles, and
they may explain necrosis of those parts. There were large differences
among species in contents. When expressed on a dry weight basis, Pinus
strobus contained more than any other species, and seven times as much
as Pinus nigra. It contained half as much per needle as Pinus nigra,
less than Pinus rigida, the same as Pinus sylvestris, and more than
Pinus montana. The different sensitivities of species could not be
explained mainly by differences in uptake rates.
Fumigation experiments of other types also have produced valuable
information. Keller and Muller (1958) found that photosynthesis and net
assimilation were depressed, while respiration and transpiration in-
creased upon exposure of three conifer species to SOp. Three to seven
week old seedlings of Pinus strobus and two other pines were injured
less by sulfur dioxide than by ozone at the same concentration (Berry
1971), while the opposite was true when older grafted plants were fumi-
gated (Costonis 1970, Houston 1974). The latter, however had been
selected for sensitivity to air pollutants, while the younger seedlings
had not; so older trees are not necessarily more sensitive. The selected
clones were injured at concentrations as low as 5 pphm. Observations in
a 10 year old white pine plantation showed that 6 pphm SO, for four
hours could cause acute injuries to some trees (Costonis T971). Suscepti-
ble trees were most sensitive during a six to eight week period when new
needles were elongating.
The sensitivity of Pinus strobus to sulfur dioxide has been compared
to other species in several fumigation experiments. Both Wentzel (1968)
and Enderlein and Vogl (1966) regard it as similar to Pinus sylvestris,
and more sensitive than Pinus nigra. This ranking makes it possible to
compare Pinus strobus to 200 other woody species fumigated and observed
in polluted regions by Ranft and Dossier (1970), and places it among the
most sensitive. Wentzel's discussion of complexities encountered in
15
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trying to compare susceptibilities of species to air pollutants are
especially useful in relating chamber fumigations to outdoor exposures.
Important variables may include pollutant type and dosage, plant age and
developmental stage, crown habit, height of the crown above ground,
foliage sensitivity, regenerative capacity, and environmental conditions.
Fertilizer applications have reduced sulfur dioxide injuries to
white pines in several studies. In an experiment with six fertilizers
and a control treatment, nitrogen increased the resistance of two to
four year old white pines, Scotch pines, and spruces (Enderlein and
Kastner 1967); deficiencies of phosphorus, potassium, magnesium, cal-
cium, and especially nitrogen increased injuries to fumigated one year
old pines. Needle tip necrosis was reduced by application of a 28-19-17
fertilizer to some sensitive clones exposed to sulfur dioxide in a
greenhouse, and also in a plantation where the ambient air contained
sulfur dioxide (Cotrufo and Berry 1970). Unfertilized ramets were
injured more severely. However, other symptoms such as banding and
mottling were not alleviated by the fertilizer treatments. In a sub-
sequent factorial fertilizer experiment using potted ramets of one clone
(Cotrufo 1974), nitrogen increased needle tip necrosis while phosphorus
reduced needle injury.
MIXTURES OF OZONE, SULFUR DIOXIDE, NITROGEN OXIDES
After unintentional exposures of white pines to air pollutants, it
is often difficult to ascertain whether single or multiple gases or
other pathological agents were the cause of injuries. Various kinds of
problems are involved in obtaining indisputable proof, despite all the
research that has been conducted. For example, in a recent episode
(Ellertson e_t aj_. 1972) ten percent of the white pines in an industrial
region were killed and many others severely injured, while others inter-
mingled with them remained healthy. The causal agent was determined to
be airborne and abiotic, but could not be identified. Sulfur dioxide
was suspected to be a contributory agent. The damage claims of Christmas
tree growers in western Maryland and West Virginia provide another
illustration (Anderson 1970, Freeman 1969). It was claimed that foliage
injuries and abnormal growth first appeared in 1967 after a new coal-
burning electric generator began operations. Several experts who exa-
mined the trees affirmed that the symptoms were typical of air pollutant
injuries. The courtroom testimony of other highly qualified specialists
was contradictory, and suggested other causes such as mites or fly ash.
The issue was not fully resolved, as there was an out-of-court settlement
in favor of the plaintiffs. The outcomes of similar cases which followed
are still pending.
In the diagnosis of post emergence chronic tipburn prior to 1960,
sulfur dioxide was suspected of being the principal toxicant, possibly
acting together with fluorides and ozone (Berry and Hepting 1964). The
16
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disease had been noted only near industrial areas which have substantial
emissions. Symptoms can develop up to 20 miles from tall stacks, so
some trees must be highly sensitive. There was no difference in sulfur
content of diseased versus healthy trees, and fluorine contents were not
high enough to cause toxicity. Yet an atmospheric physiogenic factor
was determined to be the cause. No insects or fungi associated with
diseased trees were primary causal agents. Neither fertilizing nor
pruning had any effect on the occurrence of tipburn, though in some
cases vigor was improved by fertilizing. Diseased trees recovered after
being transplanted outside the affected area. Grafting of diseased and
healthy scions on both types of rootstocks, in all combinations, caused
no change in symptoms, and disease was not transmitted to the rootstocks.
Ramets moved to an unpolluted environment recovered. Later experiments
with grafted pines demonstrated differential sensitivity of clones to
sulfur dioxide, fluorides, and oxidants (Berry 1973). Tipburn and
mottling are primary symptoms of post emergence chronic tipburn. Extensive
foliage injuries are believed to result in severe root mortality, which
in turn causes reduced needle and shoot growth and chlorosis. The
symptoms are similar to other white pine diseases. Some ways of distin-
guishing among three types of tipburn and two fungal diseases have been
described by Hepting and Berry (1961).
Semi-mature needle blight is another disease which may result from
exposure to gas mixtures, though its exact cause is still unknown (Linzon
and Costonis 1971). It is a physiogenic disease in which symptoms are
expressed by a distal reddening only in needle regions where suberization
of endodermal cells is proceeding. Symptoms resemble those of ozone
injury somewhat, but white pines susceptible to semi-mature needle
blight are more tolerant to fumigation with ozone than resistant trees
(Linzon 1966, 1967). Also the incidence of the disease does not appear
to be correlated with high ozone levels. Typical symptoms caused by
ozone or sulfur dioxide alone differ from those of semi-mature needle
blight in several ways (Linzon 1966). Intergrafting experiments have
shown that semi-mature needle blight is different from chlorotic dwarf
disease (Linzon and Costonis 1971).
Both ozone and sulfur dioxide are responsible for the chlorotic
dwarf condition of eastern white pine. The disease is common throughout
eastern and midwestern United States (Dochinger and Seliskar 1963,
1965). Chlorotic dwarf trees are sparsely foliated, and branches are
tufted due to premature shedding of all but the current year's needles
(Dochinger 1968 a, b). New foliage is light green upon emergence,
though it soon becomes mottled with chlorotic spots, and often yellowed
by early summer. Current needles are thin, curled, twisted, and may
exhibit tipburn after drought in summer or winter. All plant parts are
abnormally small. Emergence tipburn, another needle blight, appears on
some but not all chlorotic dwarf trees, and also on some "healthy" pines
(Dochinger and Seliskar 1965). This indicates that each disease is
independent of the other.
17
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Several kinds of studies have clarified the cause of chlorotic
dwarf (Dochinger and Seliskar 1970). The recovery of diseased pines
enclosed in charcoal-filtered chambers demonstrated that gaseous dis-
peroids are responsible (Dochinger et aj_. 1965). No mottling appeared,
premature needle losses were arrested, and lengths of needles and shoots
far exceeded previous ones. Trees in chambers with coarse filters or no
filters continued to exhibit chlorotic dwarf symptoms. Experiments with
grafts showed that the disease is under strong genetic control, because
healthy and diseased scions retained their original condition on opposite
rootstocks (Dochinger and Seliskar 1963). Oxides of nitrogen alone or
with sulfur dioxide cause similar damage (Skelly et^ al_. 1972). The
etiology of other physiogenic needle blights of white pine may be ex-
plained similarly by gaseous synergisms, even when levels of single
gases are insufficient to injure trees.
Fumigation experiments have shown that ozone and sulfur dioxide,
acting alone or together, cause the early symptoms of needle mottling
and defoliation in the chlorotic dwarf syndrome (Dochinger and Heck
1969). In experiments reported by Dochinger and Seliskar (1970) and
Dochinger ejt al_. (1970), levels of ozone and sulfur dioxide were too low
to produce all of the chlorotic dwarf symptoms. Mixtures caused more
typical symptoms, and more damage than the sum resulting from separate
gases at the same concentrations. Somewhat different results were
obtained by Costonis (1973), who found the greatest injury resulted
after separate exposures to each gas followed by a combined treatment.
Also, two hour exposure of sensitive clones to 5 pphm ozone plus 5 pphm
sulfur dioxide caused less injury than 5 pphm sulfur dioxide alone, but
more than ozone alone. Houston (1974) reported that sensitive clones
exposed six hours to 2.5 pphm sulfur dioxide mixed with 5 pphm ozone
sustained as much injury as at 5 or 15 pphm sulfur dioxide alone; no
symptoms developed at 2.5 pphm sulfur dioxide or 5 pphm ozone.
Susceptible seedlings fumigated up to one month by Jaeger and
Banfield (1970) were more sensitive to 5 pphm ozone than 5 pphm sulfur
dioxide. All plants exposed to mixed gases for 10 or more days devel-
oped profuse spotting on new and year old needles, plus some necrosis.
Lesions usually developed first on semi-mature tissue, then mature
tissue, and rarely on immature tissue. High humidity was much more
conducive to damage than fair weather. In another experiment by Banfield
(1972), gas mixtures caused blight at lower dosages than those of single
gases which induced symptoms. No injuries resulted from 10 pphm ozone
for four days followed by 5 pphm sulfur dioxide for four days, though
all plants exposed to a mixture at these levels developed symptoms.
Comparisons of these several experiments show they are in reasonably
good agreement. Inconsistencies probably could be explained by genetic
differences in plant materials, environmental conditions, and phenologi-
ca'l stages at which various dosages were applied.
18
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Dochinger (1970) stated, "Chlorotic dwarf exemplifies the chronic
impact that air pollution can have on our conifers. Even though we may
expect some progress in the abatement of air pollution, we must realize
that there will be an increase of damage to sensitive trees in and
around areas of urban and industrial expansion." Monitoring of pollu-
tants and injuries to white pines has provided confirming evidence. In
an Ohio plantation during the 1967 and 1968 growing seasons, 25 percent
of the days had at least 5 pphm sulfur dioxide for 2 hours; 60 percent
of the days had 5.5 pphm ozone for at least one hour; and 16 percent of
the days had 5 pphm of each gas in mixture (Dochinger e_t aj_. 1970). In
another white pine plantation (Costonis 1971), 6 pphm sulfur dioxide for
4 hours caused serious injuries to some trees on several occasions.
During the study ozone did not exceed 4 pphm, and concentrations were
not correlated with injury levels. Trees were most sensitive during a 6
to 8 week period when new needles were elongating. New symptoms of
ozone-induced needle blight in a New York plantation were detected 5
times in 1966 and 12 times in 1967 (Costonis and Sinclair 1969 b). The
highest recorded four hour mean ozone concentration preceding new symptom
development was 4.4 to 5.2 pphm in 1966 and 5.0 to 8.5 pphm in 1967.
Two kinds of control methods for chlorotic dwarf disease have been
found to be effective; genetic and environmental. Genetic variation in
susceptibility may be utilized by discarding more sensitive seedlings
during normal nursery grading practices (Dochinger 1968 b) or by select-
ing and breeding resistant varieties (Dochinger and Seliskar 1970).
Needle mottling was the best of eleven characteristics by which chloro-
tic dwarf susceptibility could be detected among seedlings. Following
selection, non-mottled seedlings were symptomatic only 5 percent of the
time and mottled seedlings were dwarfed 100 percent of the time. Appli-
cation of a high nitrogen fertilizer to white pines up to 6 feet in
height, at rates of one to four cups per tree, reduced air pollution
damage (Will and Skelly 1974). Most but not all trees responded favor-
ably, for some trees which had been severely affected by air pollutants
died after being fertilized. Although other environmental factors
besides nutrition influence responses to air pollutants, such as humidity
and temperature, they cannot be readily manipulated to reduce damage.
19
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SECTION V
BREEDING TREES FOR IMPROVED RESISTANCE TO AIR POLLUTANTS
Recognition of genetic differences between healthy white pines next
to blighted ones has led to attempts to utilize such genetic variation.
The breeding of pollution resistant varieties has been proposed, and
some white pines have already been selected. When any new plant breed-
ing program is being contemplated, it is worthwhile to consider all
information related to planning such a long undertaking. In the present
case, pertinent information from other tree species will be useful,
particularly pines and other conifers.
A question that should be raised at the outset is whether any
efforts at all should be devoted to the breeding of pollution resistant
plants. Would it not be better if all available resources were invested
in the complete elimination of noxious emissions at their sources? This
is indeed a laudable goal, but not one that is likely to be realized
soon, if ever, for reasons discussed previously. Resistance breeding
can be justified, therefore, not as an alternative to controlling emis-
sions, but as a component of a comprehensive pollution control strategy
that can be recommended in certain circumstances. If in some localities
sensitive species are likely to be damaged occasionally by phytotoxic
gases, then the most economical way of reducing damage may be by planting
more resistant varieties. The longevity and perennial habit of trees
make them especially vulnerable to rare, unpredictable pollution episodes.
For this reason they are also especially deserving of built-in genetic
protection.
Clearly defined objectives are essential for an effective breeding
program. Five kinds of goals were mentioned by Knabe (1967): (1) im-
proved resistance to major pollutants at concentrations somewhat below
those injurious to humans, (2) environmental adaptation to the region
where the improved variety will be grown, (3) resistance to other
important pathogens, (4) rapid growth and good wood quality of forest
species, (5) high filtering capacity and long life of trees planted in
urban regions. Plant breeders may need to compromise between selecting
trees that tolerate pollution best and those that absorb pollutants at
higher rates (Anon. 1974). Wentzel (1963, 1967) pointed out that there
is a practical limit to the degree to which resistance to pollutants may
be improved. He stated that even the most resistant species will succumb
to pollutants at some point. In the case of Norway spruce (which is
similar to eastern white pine in its sensitivity and variability),
Wentzel proposed that the utility of resistant varieties may be expressed
as a 20 year extension of the period during which trees remain healthy
in a region having chronic air pollution. It will be important to
resolve how the goal of pollution resistance should be set--in terms of
20
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acute exposures vs. chronic effects, and in terms of single gases vs.
mixtures. Information on other pathogens, environmental adaptation,
growth, and wood quality of white pine has been related to breeding
goals in Bingham ejt a]_. (1972) and Wright (1970).
GENETIC VARIATION IN RESISTANCE
The existence of sufficient genetic variation in resistance is
another prerequisite for success in improvment programs. Large differ-
ences have been noted between species, and also between varieties of the
same species, in their ability to thrive in polluted regions (Apel 1965,
Janson 1925, Krussman 1963). The difficulties in making such comparisons
have been discussed by Wentzel (1964, 1968). The presence of considerable
genetic variation in white pine is implied by observations of adjacent
healthy and injured trees that are commonplace in the literature. It
has been confirmed by several studies already cited, in which grafts
from healthy and injured trees retain their characteristics after subse-
quent fumigations in nature or in fumigation chambers. These reports
indicate genetic variation within populations. Variation among popula-
tions of a species and among species is also of interest. Information
on these types of resistence has been summarized by Karnosky (1974) and
Ryder (1973).
References to intra-specific variation are compiled in Table 1.
Included are eight conifers and seven deciduous species or hybrid groups,
within which significant genetic variation has been found in reactions
to one or more of four air pollutants. The studies were conducted in
North America and Europe.
There are some indications that populations from colder, dryer, or
more continental regions are less sensitive. For example, Scotch pines
from the Pyrenees Mountains were injured more by sulfur dioxide than
others from Finland (Vogl 1969). Washington and Oregon provenances of
lodgepole pine were more susceptible to sulfur dioxide than those from
Idaho and Wyoming (Lang ejt aj_. 1971, Tzschacksch et_ a 1_. 1969). In
Norway spruce, the most resistant populations came from northern regions
and high elevations (Tzschacksch and Weiss 1972). A ponderosa pine
population from Arizona was injured less than one from California (Karpen
1970). In contrast, red maples from Alabama were injured less than
populations from Pennsylvania or Minnesota (Townsend and Dochinger
1974).
Kulagin (1973) classified tolerance to gases on an ecological
basis, in attempting to predict the relative susceptibilities of plant
species. He reasoned that air pollutants are novel environmental factors,
and plants have had insufficient time for the evolution of protective
mechanisms against them. But plants do have means of protection against
21
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TABLE 1. EVIDENCE OF GENETIC VARIATION IN REACTION OF TREES TO AIR POLLUTANTS AMONG AND WITHIN POPULATIONS
ro
ro
Species
Acacia farnesia
Acer rubrum
Acer saccharum
Larix decidua, leptolepis
Picea abies
Pinus contorta
Pinus ponderosa
Differences Among
populations
populations
seedlings
families
families
clones
populations
families
populations
populations
populations
populations
populations
Pollutant
CO
°3
°3
so2
so2
S02, HF
so2
so2
S09
so2
so2
0. HF
cn n ?
bu2, u3 .
References
McMillan & Cope 1969
Townsend & Dochinger
Hibben 1969
Schttnbach et al . 1964
Enderlein et_ aj_. 1966
Rohmeder et al . 1962
Tzschacksch & Weiss 1
Enderlein et^ al_ 1966,
Enderlein & Vogl 1966
Lang et a]_. 1971
1974
, 1967
972
1967
Tzschacksch et al_. 1969
Hepting 1964
Karpen 1970
-------
TABLE 1. Continued.
ro
CO
Species
Pinus strobus
Pinus sylvestn's
Platanus
Populus hybrids
Populus tremuloides
Pseudotsuga menziesii
Ulmus americana
Differences Among
clones
clones
clones
populations
clones, families
families
clones
clones
clones
clones
populations
families
clones
Pollutant
°3> S02
HF, 03, S02
HF, S02
so2
so2
°3' S02
so2
so2
°3
°y S02
S09
o3, so2
°3' S02
References
Houston 1974
Berry 1973
Rohmeder et al . 1
Vogl 1969
Vogl 1970
Santamour 1969
Dochinger et al .
Lampadius et al .
Wood & Coppolino
Karnosky 1974
Enderlein & Vogl
Santamour 1969
Karnosky 1974
962
1972
1970
1972
1966
-------
adverse natural conditions such as drought, frosts, leaf-damaging pests,
and possibly volcanic gases. These might preadapt plants so that they
are tolerant or resistant to effects of air pollutants. Examples of
such mechanisms may include thick epidermis or waxes which limit gas
exchange of leaves, compact internal tissues, closing of stomata during
drought, and plant habits which reduce contact between leaves and gases.
Relationships have been found between ozone sensitivity and leaf morphology
and anatomy of four California pines (Evans and Miller 1972). Low
sensitivity was correlated with fewer stomata and more constricted
cavities, suggesting that resistance is related to limited gas exchange.
The resistance of some spruces to sulfur dioxide may be due to their
ability to produce greater amounts of wax and thus lower diffusion of
gases through stomata (Hartel and Papesch 1955). Near an industrial
plant that emitted sulfur dioxide, the amounts of wax on healthier trees
increased when gas concentrations were higher, and reached levels never
observed under natural conditions. Trees that showed acute damage had
normal or slightly elevated amounts of wax. Variations in sulfur content
of needles may reflect differences among individuals in gas uptake rates
(Themlitz 1960). Biochemical characteristics have also been investigated
as indicators of relative resistance, such as oxidizability of cell
contents (Antipov and Chekalisnkaya 1966) and essential oils (Cvrkal
1959).
Various possible types of resistance to sulfur dioxide were classi-
fied by Vogl et^ aj_. (1965), and physiological implications for breeding
were discussed. Some of these cause reduced uptake of sulfur dioxide,
and others reduce injury of leaves or entire plants despite exposure of
cells to high pollutant levels. Certain ones can be useful to breeders,
while others may complicate selection if they are not taken into account.
SELECTION METHODS
There are several ways of comparing relative sensitivities of trees
in order to select the most resistant ones for propagation or breeding.
Indirect selection for physiological, anatomical, or morphological
traits correlated with resistance could be practiced. However, it is
likely to be less effective than direct selection for resistance^unless
all correlated traits are completely understood, and also more easily
measured (Gerhold 1972).
The safest procedure is to select the healthiest of trees that have
been exposed repeatedly to air pollutants in nature, based on performance
of whole plants similar in age and environmental conditions. This
approach has been used successfully with Norway spruce and Scotch pine
(Rohmeder et_ al_. 1962, Rohmeder and von Schflnborn 1965, 1967, 1968); and
eastern white pine (Houston 1974, Houston and Stairs 1973). Repeated
observations of crown damage to spruce trees over a period of years
24
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indicated that most individuals remained in the same resistance category,
though some shifts in both directions were noted (Lampadius ejt aj_. 1970,
Wentzel 1967). Some trees that at first seemed resistant later died.
In older forests dominant trees generally were more sensitive than co-
dominant trees. In younger stands suppressed trees were killed by
pollutants before more successful competitors. The resistance of trees
that have been selected in this manner needs to be ascertained by subse-
quent fumigation tests using progeny or vegetative propagules.
Another method is to fumigate many trees when they are small, and
then retest the more resistant ones when they are older. This makes it
possible to achieve higher selection intensities under better controlled
conditions. Young white pines have been selected sequentially for
resistance to sulfur dioxide from a power station, fluorides from a
fertilizer plant, and oxidants from vehicular traffic (Berry 1973). Of
1428 survivors from 2400 seedlings, 4.5 percent were resistant to all
three types of pollutants. By using fumigation chambers, many more
exposures per year are possible and environmental conditions may be
carefully controlled.
Conventional chambers have been used for many of the studies in
Table 1. In others, specially designed outdoor chambers were employed
that simulate real conditions more closely. Gerhold et^ al_. (1972)
developed a tubing fumigation system which is especially suited for
estimating genetic parameters needed for a breeding program.
Rapid tests in which detached plant parts are fumigated may be
useful for making initial selections or for experimental purposes. A
method for fumigating excised twigs was developed for Larix (Bortitz and
Vogl 1965) and later adapted to Pinus (Vogl and Bortitz 1968). A similar
technique employs excised pine needle fascicles (Schtltt et_ al_. 1970).
More precise results can be achieved if effects of dosage, growth
stage, environmental conditions, and other non-genetic variables can be
defined, as has been done with Virginia pine exposed to ozone (Davis and
Wood 1973 a, b). In the absence of such information, or because of it,
several investigators have recommended that plants be fumigated on
several dates during the growing season (Demeritt ejt aJL 1971, Tzschacksch
et^ aj_. 1969, and others). Better estimates of resistance levels can be
derived from repeated exposures, because these take into account inter-
actions of genotypes with varying environments, and reduce random variabil-
ity.
Data from fumigation experiments commonly are characterized by
binomial rather than normal frequency distributions (Demeritt et al.
1971, Tzschacksch 1972). These may be caused by deviations from optimum
fumigant dosages, different resistance levels or types, climatic variables,
or nutrition levels. The distributions may have important implications
for experimental design, data analysis, and plant selection.
25
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INHERITANCE OF RESISTANCE
Estimates of the degree of genetic control over variation in resis-
tance are rare. Genetic information is needed for designing efficient
selection procedures and for predicting the amount of improvement that
can be achieved through alternative breeding methods.
The upper limit of genetic control for tolerance to sulfur dioxide
and ozone was estimated by clonal repeatability analysis of white pines
exposed in greenhouse fumigation chambers (Houston and Stairs 1973).
Selected tolerant and sensitive clones were exposed 6 hours to 2.5 pphm
sulfur dioxide and 5 pphm ozone. Repeatability estimates of 0.5 for
needle elongation and 0.8 for needle injuries indicated strong genetic
control. The results suggest that resistant individuals could be iden-
tified in the field with little error. Nothing has been reported about
genetic transmission of resistance to offspring in white pine.
A similar study by Karnosky (1975) gave evidence of strong genetic
control of response to sulfur dioxide and ozone by trembling aspen.
Clonal repeatability estimates were 0.5 for sulfur dioxide plus ozone,
and 0.6 for each of the gases applied singly.
Grafted Scotch pine clones and their progenies have been compared
in sensitivity to sulfur dioxide (Vogl 1970). Significant differences
were found among clones and among families. Clones had been selected
previously by rapid tests. There were large differences among some
families obtained by mating two males to each of six females. The
family means suggested the possibility of specific combining ability,
though general and specific components were not reported. High correla-
tion between clone values and offspring values was implied, but not
supported by the data.
Demeritt and Gerhold (Unpublished ms.) derived heritability esti-
mates from 30 open pollinated Scotch pine families representing a single
population. Seedlings in a nursery were fumigated separately with ozone
and sulfur dioxide on several dates. The variance components estimated
from needle injury data indicated moderate to strong genetic control.
Experiments with other populations indicated weak to moderate gffnetic
control. In a related study (Demeritt et aK 1971), ozone injuries were
weakly and positively correlated with sulfur dioxide injuries, and
neither was correlated with height of seedlings. Thus it should be
possible to select effectively for both types of resistance, with no
adverse effects of growth rate. Discontinuities in the distributions of
injury scores suggested that few genes or different mechanisms may
govern resistance.
26
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BREEDING AND PROPAGATING METHODS
°f methods ™y be employed in designing a com-
c C lo?0*1"9' Ceding, and mass producing resistant
? ( h f. 196?]- Severa1 tree improvement programs have been
. ln_whlch resistance to air pollutants is a main objective. They
th f/ar!y stages of development, so it would be premature to compare
tne ei-Tectiyeness of alternative methods. However, there are indications
that worthwhile progress is being made.
The development of Norway spruce and Scotch pine varieties with
improved resistance to industrial fumes started about 1956 in West Germany
(Rohmeder et aj_. 1962, Rohmeder and von Schtinborn 1965, 1967, 1968,
Wentzel 1967). Phenotypically resistant trees were selected in severely
damaged forests and propagated by grafting. Subsequent fumigation tests
with S02 and HF showed that selection had been very effective for Norway
spruce, and to a lesser degree also for Scotch pine. When injury levels
of selected clones were tested, they were found to be far below those of
normal grafts or seedlings used for comparison. They were also injured
less than several deciduous species that are generally considered less
sensitive, though the practical implications of this have been disputed
by Wentzel (1967). Trees that were selected for resistance to SO-
generally were also resistant to HF, and vice versa. The Norway spruce
clones are being propagated by rooted cuttings. Seed orchards have been
established by grafting for the production of seed-propagated varieties
that can be planted in industrial regions.
A combination of selection methods that would be suitable for im-
proving sulfur dioxide resistance in larch possibly also Scotch pine has
been proposed by Pclster et. aj_. (1965). The leaves are regarded as the
most important plant part for expressing resistance. Rapid tests are to
be used for initial selections of parent trees. Selected trees are
mated, and their progenies fumigated in outdoor chambers. The best
families are then planted in industrial regions for further selection
according to resistance and growth rate. The best parents may be grafted
into seed orchards. Seeds for the growing of resistant varieties could
be harvested ten years after selection started.
Seedl ings of Larix decidua and L_. decidua x leptolepis were eval-
uated for resistance to sulfur dioxide in fumigation experiments and
field plantings (Enderlein et. al_. 1966, 1967, Schttnbach et_ al_. 1964).
The most resistant families in fumigations were hybrids. These were
also injured the least and grew tallest in forest conditions. The re-
sults are encouraging, in that juvenile selection and seed propagation
seem to be feasible, though further confirmation at more advanced ages
is needed.
27
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Nine poplar clones were compared in field trials and fumigation
chambers at four dosages of sulfur dioxide (Lampadius et^ al_. 1970). The
most resistant one and the least resistant two had consistent performances,
but others varied widely. It was concluded that young plants in fumigation
experiments are imperfect predictors of resistance expressed in forests.
Interaction of genotypes with environments is one of the reasons.
Another is reliance on leaf injuries, which do not adequately measure
recovery and growth of whole plants after injury. Nevertheless, it is
acknowledged that fumigation experiments have utility for initial selection.
DSssler (1967) conducted a similar study with five poplar clones
and eleven conifer species, comparing potted plants in fumigation chambers
to exposures under forest conditions. The results compared favorably,
indicating that short, acute exposures are useful for experimental
purposes.
The reliability of rapid tests of sulfur dioxide resistance was
evaluated using four of 16 Scotch pine clones (Vogl and Bortitz 1968).
The two most resistant and the two least resistant, selected according
to rapid tests, were compared under various conditions. The ranks re-
mained the same after exposure to 0.6 ppm for several days, to 200 ppm,
and at various seasons with different weather conditions.
All of the tree improvement projects mentioned so far are European
ones. The main efforts in the United States have been directed toward
white pine (Berry 1973, Houston and Stairs 1973), Scotch pine (Gerhold
and Palpant 1968), loblolly pine (in 17th Annual Report, Cooperative
Tree Improvement and Hardwood Research Programs. School of Forest
Resources, North Carolina State University 1973, pages 50, 51), and red
maple (Anon. 1974). The work on white pine consisted mainly of selection,
vegetative propagation, and testing, as described previously. Little
has been published on the other species, except for Scotch pine.
The breeding objectives, selection methods, and information needed
for the design of a Scotch pine breeding system were described by Gerhold
and Palpant (1968). The goals of the program were to maximize resistance
to sulfur dioxide and ozone, to maintain the environmental adaptability
of varieties commonly used in northeastern United States, and to exploit
remaining variability in ornamental qualities on an opportunistic basis.
Several hundred artificial matings were made among trees from diverse
geographic origins, extending from Scotland to Siberia, and Spain to
Sweden (Karrfalt et_ aJL 1976). Seedlings from the initial matings have
been selected after fumigation tests conducted under nursery conditions
(Demeritt et^ al_. 1971, Gerhold ejt aj_. 1972). Further progress is uncer-
tain because of a lapse in financial support.
28
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Research needs related to pollution-resistant trees for north-
eastern United States were analyzed recently (Gerhold, H. D. 1976).
Long-term research is needed on six questions:
1. Which of the commercially available species and cultivars
can be recommended for planting in polluted localities?
2. In which species should genetic improvement projects be
started?
3. What methods are most effective in selecting for pollu-
tion resistance? Subsidiary questions involve selection
criteria, frequency and season of exposures, environmental and
age effects, fumigation dosages and gas mixtures, and types of
fumigation chambers.
4. What is the best way of searching for resistant genotypes?
5. Which breeding methods and mating designs are most effec-
tive for creating improved varieties?
6. Which propagation methods are most appropriate for mass
producing new varieties?
These questions are inter-related. Priorities for research can be
set most logically by considering the relative sensitivities of species,
their values in plantings, and the probable success of breeding projects
in operational and commercial contexts. Several experts who have reviewed
related literature have recommended research on improving the genetic
resistance of trees to air pollutants (Doolittle 1969, Heck et_ a]_. 1973,
Kisser 1966, Knabe 1972, Sinclair 1969). These kinds of research are
not likely to be carried out unless substantial, long-term support is
provided by Federal agencies responsible for reducing pollution damage
to timber and landscape species.
29
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SECTION VI
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30
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12. Bernatzky, A. 1968. Schutzpflanzungen zur Luftreinigung und
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31
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23. Botkin, D. B.t W. H. Smith, R. W. Carlson, and T. C. Smith. 1972.
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25. Costonis, A. C. 1970. Acute foliar injury of eastern white pine
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26. Costonis, A. C. 1971. Effects of ambient sulfur dioxide and ozone
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32. Cotrufo, C. 1974. The sensitivity of a white pine clone to air
pollution as affected by N, P, and K. USDA For. Serv. Res. Note
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33. Cotrufo, C. and C. R. Berry. 1970. Effects of a soluble NPK ferti-
lizer on sensitivity of eastern white pine to injury from SO, air
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34. Cvrkal, H. 1959. Biochemicka diagnoza smrkv v kourovych oblastech
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32
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35. Dossier, H. G. 1967. Zur Aussagekraft experimentaller Resistenz-
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36. Davis, D. D. 1970. Temperature relative humidity affect sensitivity
of plants to air pollution. Sci. in Ag. 18(1):7.
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two tree species to ozone. Phytopath. 58:399. (Abst.)
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eighteen coniferous species to ozone. Phytopath. 62:14-19.
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dioxide interaction. Nature. 225(5231):476.
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47. Dochinger, L. S. and C. E. Seliskar. 1963. Susceptibility of
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404-407.
33
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49. Dochinger, L. S. and C. E. Seliskar. 1970. Air pollution and the
chlorotic dwarf disease of eastern white pine. Forest Sci. 16(1):
46-55.
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of chlorotic dwarf of eastern white pine. Phytopath. 55:1055.
(Abst.)
51. Dochinger, L. S., A. M. Townsend, D. W. Seegrist and F- W. Bender.
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34
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36
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2
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44
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-60Q/3-77-OQ2
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
EFFECT OF AIR POLLUTION ON PINUS STROBUS L. AND
GENETIC RESISTANCE - A Literature Review
5. REPORT DATE
January 1977
x$
=IM
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
8. PERFORMING ORGANIZATION REPORT NO.
Gerhold. H.D.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
The Pennsylvania State University
University Park, PA 16802
10. PROGRAM ELEMENT NO.
1A1006
11. CONTRACT/GRANT NO.
P5J10505-J
12. SPONSORING AGENCY NAME AND ADDRESS
Corvallis Environmental Research Laboratory
200 SW 35th Street
Corvallis, OR 97330
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/ORD
15. SUPPLEMENTARY NOTES
16. ABSTRACT
Effects of the main phytotoxic gases that injure eastern white pine (Pinus strobus L,
and the possibilities of breeding resistant trees are discussed in a comprehensive
literature review. The main purpose of the report is to summarize knowledge which
may be used in providing protection to a valuable species. Implicitly related
topics are reviewed briefly, including sorption and emission of gases by plants,
air quality standards, bioindicators for monitoring air quality, and silvicultural
measures for protecting trees against injuries.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
1. Eastern White Pine (Pinus Strobus-L.)
2. Pollution (S02, Og, and N02)
3. Resistance
4. Breeding
1. Breeding for resistance
2. Air pollution effects
3. DISTRIBUTION STATEMENT
Release to Public
19. SECURITY CLASS (This Report)
Unclassified
20. SECURITY CLASS (This page)
Unclassified
21. NO. OF PAGES
50
22. PRICE
EPA Form 2220-1 (9-73)
45
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