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CHAFHP.6 Ample proof exists that plants have been injured by changes in the character of the environment, especially by air pollution (Jacobson and Hill 1970). Vegetation injured by pollution may be killed or visibly damaged, or the effects may be more subtle, such as reduced growth or yield, decreased reproductive success, or lowered resis- tance to disease, drought, or other stresses. Seme current environmental problems, such as chronic low-level air pol- lution by photochemical oxidants or the increased acidity of rainfall, may have effects on vegetation over extensive geographical areas. Such effects on plants could lead to changes in the stability or productivity of agricultural, forest, or other ecosystems. t The predominant emphasis in research on injury to vegetation has been on the effects of air pollutants on agricultural crops and on trees. The experience of this panel, and thus the recommendations of this chapter, reflect that emphasis. Other kirds of vegetation may also be affected by pollution, hcwever, and those effects may have important ecological and economic consequences.' Although they are not dealt with further in this chapter, we feel that several additional areas of research deserve continued or increased interest and support. These include studies of the effects of air and soil pollutants on lichens, fungi, grasses, shrubs, and other native vegeta- tion; investigations of the effects of water pollutants on algae and other aquatic plants; and studies of the effects of environmental contaminants on ornamental plants. In particular, research on effects en algae deserves high priority, both because of the important ecological role played by algae and because of the dearth of information about algal responses tc most toxic pollutants. A great deal of research has been conducted on the acute effects on a variety of agricultural and forest plants of some air pollutants (chiefly sulfur dioxide, ozone, and fluoride). Several estimates are available of chronic damages, primarily due tc photochemical oxi-
dants (NFC of Canada 1975). Dose-response data are simply not available, however, for the chronic effects cf most contaminants, especially on natural plant communities and ecosystems. To develop the information it needs for decisions such as establishing or revising secondary air quality standards, EPA will need to draw on the experience and resources of many elements of the plant research com- munity. Major contributions to research on effects of environmental contaminants on vegetation have been made by universities, nonprofit research institutes, and government laboratories, with funding largely from USDA, EPA, NSF, pri- vate industry, and utilities; this diversity in research should continue. To avoid unnecessary duplication cf effort, sponsors of research should encourage timely reporting of research results, Eefcre relationships between environmental contaminants and vegetation damage in agricultural and forested areas can be determined, the concentrations and trends over time for important pollutants in those areas mist be measured. The environment in or near urban and industrial locations has been extensively monitored, but there has been no coor- dinated effort to provide a continuous record of pollutant levels in agricultural and forested portions of the coun- try. Improved monitoring is needed in order to estimate ,the effects of pollution on plant communities or to enforce nondegradation policies or similar protective measures (Miller et al. 1972). The most important phytotoxic pollutants to monitor are ozone and sulfur dioxide, which row cause and will probably continue to cause the greatest amounts cf injury to vegeta- tion, at least within the United States. It might also be useful to monitor peroxyacetyl nitrate (FAN), fluorides, and nitrogen dioxide in specific rural locations, and rcany ether chemical pollutants or trace substances, as appropriate, near specific sources. The hydrogen ion content (pH) of rainfall, which is determined by the kinds and amounts of anions and catiors contained ir precipitation, may have significant phytotoxic and ecological effects. Increased monitcring in remote areas of both acidity and the concentrations of specific ionic components of wet and dry precipitation is needed to support studies of the effects of acid rainfall on agriculture and forestry. A coordinated nationwide program of monitoring of air quality and of the composition of precipitation in agricul- tural and forested areas should be undertaken. A review of monitoring needs has been conducted concurrently with this project by the Study Group on Environmental Monitoring cf the NRC, and their report should be consulted for additional - 75 -
recommendations and discussion of monitoring requirements and methods (NRC 1977). LABORATORY STUDIES CK FHYTOTOXICITY Efforts should be expanded to develop se_data,fo£ S.SX2-Elaa£i«. t§_undey con- Basic dose-response data are still needed on the effects cf most environmental contaminants on plants, especially for long-term, low-level exposures (Larsen and Heck 1976). Indoor studies that attempt to simulate outdoor growing conditions provide models of effects of pollutants, which can then be tested in the field. Plant populations in the field are influenced by many natural variables, including light, temperature, air and soil moisture, soil nutrients, insects and pathogens, and physiological states (seasonal changes and life-cycle phases) . The effects of exposure to one or more pollutants are usually superimposed on effects due to other stresses, so that it is difficult to assign a particular cause to observed chronic adverse effects. The chief advantage of laboratory testing is that the inter- actions among several such stresses (including mixtures of pollutants) can be studied by varying one factor at a time. Although elaborate chamber studies have been conducted in a number of institutions for many years, significant opportunities to advance the sophistication of research methods still exist. For example, programmable or compu- ter-controlled exposure chambers can be used to vary one or more factors and more closely simulate actual stress conditions (McLaughlin et al. 1976, Doshi 1975). The study of dynamic, multivariate systems is a promising direction for future research. Laboratory research would best be accomplished in those government agencies, ncnprcfit research institutes, and agricultural experiment stations that have the neces- sary facilities and experience to conduct complex chamber studies. Funds should be provided by EPA, OSDA and the Forest Service (USFS) , EPDA, and other interested public cr private sources. - 76 -
FIELD STUDIES OF VEGETATION DAMAGE Eroductivitv under actual gr owi ng_con di t ion s . Eecause no laboratory study, no matter how sophisti- cated, can duplicate the actual conditions plants encounter in the outdoor environment, measurements in the field of injury to vegetation are essential. The soundest assessment of the actual risks pollution represents to crops, forests, and ether plant communities is one based on mutually con- firming results of indoor and field studies. Some promising techniques have been developed fcr making quantitative measurements cf the effects of air pollutants on crop productivity. Field plots can be covered with enclosures that exclude pollutants (by fil- tration) but make minimal changes in other environmental conditions (Mandl et al. 1973). Measured amounts of pol- lutants can also be added to suck enclosures, or to field plots with ro enclosures (Lee et al. 1975). Effects of exposing vegetation to a given pcllutart concentration in the laboratory can thus be compared with effects of the same known concentrations under field conditions. Field studies and indoor experimental research must be closely coordinated tc ensure comparability of results. Unfortunately, the research teams and institutions that are best prepared to do large indoor studies may not be experienced in field research techniques. Programs should te designed that incorporate both elements. Here, too, support should be provided from EPA, USDA, USFS, EREA, and ether interested public or private sources. MECHANISMS OF PHnOTCXICITY be_intersif ied_gn mechanisms._gf._action of toxic er.yj.r- Lack of knowledge of the metabolic and physiological mechanisms of toxic effects of pollutants on plants hinders the achievement of several important objectives. Perhaps the most significant of these is the development of prac- tical, reliable bioassay techniques for detecting injury to vegetation in the field on the basis cf physiological indicators. Present measures cannot reliably distinguish - 77 -
metabolic responses of plants to pollutarts from responses to other stresses, such as ccld cr drought. By the time more reliable indicators of toxicity such as visible foliar injury or reduced growth appear, dan-age may be irreversible. A better understanding of the physiological mechanisms cf toxicity could make it possible to detect injury at a time when corrective action might still be possible. Research of this kind should also advance understanding in such problem areas as breeding pollution-resistant varie- ties of plants, assessing the effects of interactions among multiple toxic agents and other stresses, anticipating the impacts of new pollutants, extrapolating estimates of injury from one species of plant to others that metabolize a con- taminant in the same way, and determining the utility of the threshold concept for damage to vegetaticn. Ihe elucidation of mechanisms of phytotoxicity is likely to be accomplished best through long-term research efforts in universities, private research foundations, and the few government laboratories that study fundamental problems of plant physiology. At present, the demand for dose-response data and other information of immediate value is great. In contrast, support for more basic investigations of mecha- nisms has become increasingly limited. Greater funding in this area should be encouraged; it might most reasonably be provided through NSF or other granting agencies that are not mission-oriented. - 78 -
Coshi, Y.K. (1975) Design of a digitally controlled environ- mental chamber for air pollution effects studies on plants. Report EES-511X-1. Columbus: Ohio State University. Jacobson, J.S. and A.C. Hill, eds. (1970) Recognition of air pollution injury to vegetation: A pictorial atlas. Pittsburgh, Pa.: Air Polluticn Centro! Association. Larsen, R.I. and W.w. Heck (1976) An air quality data analysis system for interrelating effects, standards, and needed source reductions: Part 3: Vegetation irjury. Journal of the Air Pollution Control Association. 26:326-333. Lee, J.J., R.A. Lewis, and D.E. Eody (1975) A field experi- mental system for the evaluation of the environmental effects of sulfur dioxide. Pages 608-629, The Fort Union Coal Field Symposium, edited by w. Clark. Bozeman, Mont.: Montana Academy of Sciences. McLaughlin, S.B., V.J. Schorn, and H.C. Jones (1976) A programmable exposure system for kinetic dose-resporse studies with air pollutants. Journal of the Air Pollution Control Association 26:132-135. Mandl, R.H., L.H. Weinstein, D.E. McCune, and M. Keveny, (1973) A cylindrical, open-top chamber for the exposure of plants to air pollutants in the field. Journal of Environmental Quality 2:371-376. Miller, P.R., M.H. McCutchan, and B.C. Ryan (1972) Influ- ence of climate and topography on oxidant air pollution concentrations that damage ccnifer forests in southern California. Mitteilungen der Forstlichen Bundes- Versuchsanstalt (Wein) 97:858-607. - 79 -
National Research Council (1977) Environmental Monitoring. Analytical Studies for the U.S. Environmental Protection Agency, Volume IV. Peport of the study Group on Environmental Monitoring. Committee cn National Statistics, Assembly of Mathematical and Physical Sciences. Washington, D.C.: National Academy of Sciences. National Research Council of Canada (1975) Photochemical air pollution: Formation, transport and effects. Ottawa, Canada. - 80 -
