DM. Olszyk (USA) and K.T. Ingram (Philippines)
The U.S. Environmental Protection Agency (EPA) and International Rice Research Institute (IRRI) are initiating a cooperative program on the effects of UV-B and global climate change (increased CO2 and temperature) on rice. Rice is the world's most important food crop and responds both to UV-B and climate change. The project will determine:
1. The effects of these stresses on the rice ecosystem.
2. The extent and intensity of those effects for Asia.
3. The importance of the rice ecosystem as a source of biogenic emissions such as methane and the impacts of environmental stress on those emissions.
4. Mitigation/adaptation options available to reduce any effects on rice yields and biogenic emissions.
Scoping studies will produce UV-B and climate change scenarios for tropical rice growing areas. Experimental studies will be conducted in controlled environments and field plots to evaluate the sensitivity of genotypes, dose-response relationships, and other responses of rice to UV-B and global climate change. Complementary studies will determine the effects of these stresses on rice ecosystem components such as diseases and insects. Investigations will be made of methane emission rates from rice fields, and how those rates would change with climatic change. Models of rice plant processes and ecosystem structure and function will be used for predictive purposes and regional impact assessments. Ultimately, assessments based on modeling will provide options for policy makers and rice producers to mitigate the effects of UV-B and global climate change on rice production.
Causes of UV-B and Global Climate Change
The fundamental goal of this research program is to accurately assess the risks of UV-B and global climate change to the tropical wetland rice ecosystem. This goal is being addressed through a partnership between the U.S. EPA's Environmental Research Laboratory at Corvallis (ERL-C) and the world's preeminent research institute for rice, the International Rice Research Institute.
Although Earth's atmosphere is composed primarily of nitrogen (N2) and oxygen (O2), the dynamics, structure, and chemistry of the atmosphere is influenced greatly by a number of other gases which exist in very small (trace) quantities. Chief among the effects of these gases is the trapping of solar energy at the Earth's surface in the form of heat. Such gases are often termed greenhouse gases because they trap solar heat just as greenhouse glass does. The concentrations of these gases have a powerful influence on the average global temperature of the planet, and consequently, on the global climate.
One class of atmospheric trace gases, the chlorofluorocarbons (CFCs), have an important additional effect on the atmosphere; their photodegradation products act to destroy ozone (O3) in the stratosphere. Ozone is a strong absorber of solar ultraviolet radiation, and the stratospheric ozone layer acts to filter out much of the ultraviolet component of the solar spectrum before it penetrates to the Earth's surface. Thus, depletion of stratospheric O3 allows more solar UV to reach the earth's surface.
Figure 1 indicates the estimated stratospheric ozone depletion in Asia tor 1969 1987. A 1-4% ozone decline was calculated for most rice growing areas. Special considerations regarding these estimates are as follows:
1. Under clear-sky conditions, the ambient UV-B flux in tropical rice-growing areas is already among the highest on the Earth's surface because the stratospheric ozone layer is naturally thinner than at high latitudes, and because solar angles are higher. Thus, with stratospheric ozone depletion, the UV-B flux in tropical areas is likely to exceed that experienced anywhere in the world.
2. Clouds can reduce UV-B transmission through the atmosphere. Thus, in the tropics where there is a strong monsoon-driven seasonality in cloud cover, actual UV-B radiation during certain times of the year may be lower than predicted for clear skies. However, the quantitative effects of clouds on UV-B have not been clearly determined
In addition to CFC's, concentrations of other greenhouse gases such as carbon dioxide (CO2) and methane (CH4) have increased significantly in Earth's atmosphere since preindustrial times.
(a) A doubling of atmospheric CO2 concentration to over 6OO ppm is predicted within 100 years.
(b) The actual rate of CO2 increase will vary depending on the magnitude of the increase in future emission rates for CO2 and carbon cycling feedbacks with the atmosphere, oceans, and biosphere.
Recent efforts to define the scope, direction, and magnitude of the likely climatic changes have involved the use of massive mathematical climate simulation models. Several different GCMs have been developed and are in use
Because the models rely on slightly different atmospheric parameters, and make different operating assumptions, their predictions are not perfectly congruent. The models agree, however, that:
(i) Global air temperature generally is predicted to increase by 3 to 5deg.C with a doubling of atmospheric CO2 (Schneider, 1989).
(ii) Air temperatures in rice producing areas of south and east Asia are predicted to increase from O to 7deg.C depending on month and model used.
Whatever the magnitude of the predicted temperature changes, the pattern of temperature increase would vary over tropical rice producing areas depending on geographical factors Rainfall patterns also would be expected to change depending on changes in temperature, which could have profound impacts on rice production. However, precipitation changes are difficult to predict on a regional basis and are beyond the scope of this report
Importance of Rice
Changes in global climate would significantly affect human health, natural aquatic and terrestrial ecosystems, and agricultural ecosystems. World-wide attention recently has turned to these issues and scientists from many disciplines and many countries are working to assess the potential magnitude and direction of the changes and the risks to the biota. Of great immediate concern to policy makers and scientists worldwide, are the potential effects of the changes on the world's agriculture. To meet the demands of a growing human population, agricultural productivity must continue to increase. If global climate changes, act to reduce food production, serious, long-term food shortages and aggravation of societal problems could result.
Of all the world's crops, rice is the most important for direct human consumption:
(i) It is the staple food for over half of mankind, with at least 2 billion people in Asia alone depending on rice for much of their daily caloric intake (Figure 2).
ii) Due largely to the introduction of improved, high-yielding rice varieties by the IRRI in the Philippines, and to the increasing availability of chemical fertilizers, world rice production has increased steadily in the last two decades, managing to keep pace with population growth. In the last five years, however, production growth has ceased.
(iii) By the year 2000, almost two-thirds of the world's population will depend on rice as their primary food source, if the population growth of developing countries continues at the present rate.
More than 90% of the world's rice production is in Asia, primarily in an area from approximately 40deg.N latitude to 10deg.S latitude, including 19 countries (Figure 3). China and India grow the most rice, with 41% and 20% of the Asian production, respectively, in 1985-87 (IRRI, 1989). Nearly 3/4 of rice production is from irrigated fields, especially in China.
Enhanced UV-B and global climate change will impact tropical rice growing regions. Although temperature changes induced by global warming should be more dramatic, at least initially, at higher latitudes than in the tropics, tropical warming should become pronounced by early in the next century (Hansen et al, 1988), with significant changes in regional weather likely. Increases in UV-B radiation are also likely due to ozone depletion. As with temperature changes, the most dramatic percentage decreases in stratospheric ozone are predicted to occur at high latitudes, but because the ozone layer at the equator is naturally much thinner than at higher latitudes (a consequence of stratospheric air circulation), relatively small decreases in the ozone layer over the tropics may cause significant increases in UV-B.
Rice Response to UV-B and Climate Change
UV-B effects on rice plants
UV-B radiation has been demonstrated to affect some aspects of human health, aquatic ecosystems, and agricultural and natural terrestrial ecosystems. Effects of UV-B on terrestrial biota, both direct and indirect, have been demonstrated at every level of biological organization (Figure 4), from plant molecules to entire ecosystems. Among the observed effects are:
1. A number of plant molecules, such as DNA, lipids, and proteins strongly absorb UV-B and can, in turn, induce specific changes in tissue and whole-plant structure and function (Caldwell et al, 1989);
2. UV-B can reduce plant growth and yield through reductions in biomass production, seed yield, and yield quality (Barnes et al, 1988).
3. UV-B can alter plant morphology through reductions in plant height and leaf area, increased tillering, and changes in plant geometry (Barnes et al, 1988).
4. Plant physiological processes are impacted by UV-B. Photosynthesis is often reduced, and the production of plant secondary metabolites increased (Renger et al, 1989; Caldwell et al, 1989).
5. Plant competitive interactions can shift due to the differential sensitivity of competing plant species (Fox and Caldwell, 1978; Barnes et al, 1988).
6. Pest-pathogen relationships may be altered due to changes in plant secondary metdbolites (Caldwell et al, 1989).
Few studies have been conducted on the effects of UV-B radiation on rice, and current information is insufficient to support an assessment of the risks of UV-B to rice production. Research is currently underway at the IRRI in the Philippines and at the EPA's Corvallis Environmental Research Laboratory to fill the critical data gaps and to support the risk assessment process. Among the direct effects of UV-B that have been observed in both previous and ongoing studies are:
a) There was a possible trend towards a reduction in seed yield for one rice cultivar under enhanced UV-B conditions in the field simulating ozone depletions of 8 to 16% for Florida, USA. However, the results were highly variable and the UV-B effects were not statistically significant (Figure 5, Biggs et al, 1984).
(b) The effect of UV-B enhancement on rice yield under tropical conditions, where ambient solar UV-B levels are among the highest on earth, has yet to be examined.
(c) Rice growth and photosynthesis can be suppressed by exposure to UV-B under greenhouse conditions. However, few cultivars have been examined and no studies have examined photosynthesis responses under field conditions where plants are generally more tolerant to UV-B enhancement (Research in progress at ERL-C).
(d) UV-B can induce the accumulation of UV-absorbing pigments and alter leaf surface characteristics. It is unknown whether these responses are sufficient to completely protect rice from increased exposure to UV-B or whether variation in these traits is related to variation in cultivar sensitivity to UV-B-induced injury (Research in progress at ERL-C).
(e) In some cultivars, UV-B can alter plant morphology without reducing plant biomass. Since some of these morphological traits, such as tillering, are known to influence rice yield, UV-B could potentially alter grain yield without apparent reductions in total production (Beyschlag et al, 1988).
(f) Substantial variation appears to exist in both the magnitude and direction of UV-B-response among rice cultivars. Preliminary studies by Vergara at IRRI indicated that although UV-B generally acted to reduce plant weight, the magnitude of response was highly cultivar-dependent (Coronel et al, 1990). Thus, identification and/or breeding of UV-B-tolerant cultivars may be an important means of adapting to the potential effects of ozone depletion.
UV-B effects on the rice ecosystem
UV-B radiation is likely to have important indirect effects on rice production through effects on other biotic components present in the rice ecosystem, i.e., important organisms including rice, and key rice weeds, diseases, insects, and nitrogen-fixers. Important effects may include:
I . Results from pilot experiments indicate that UV-B enhancement can significantly increase the susceptibility of rice to blast disease. The increased potential for blast disease severity due to UV-B enhancement would exacerbate an already significant disease problem (M. Bonman, personal communication).
2. Competition from weeds can reduce rice yield 75% and weed-control measures cost millions of dollars annually. UV-B enhancement is known to alter the competitive balance between crops and weeds, with grass-grass mixtures likely to be most affected (Barnes et al, 1988). Because the principal weeds of rice are other grass species, there is strong reason to believe that competitive balance between rice and major weeds could be altered under enhanced UV-B conditions.
Effects of CO2 and temperature on rice plants
There have been many experiments on direct effects of CO2 or temperature separately that indicated potential changes in rice growth and productivity from global climate change. A doubling of atmospheric CO2 concentration to approximately 660 ppm could produce beneficial effects on rice including:
I . Increases in grain production by 6-50% depending on cultivar and experimental conditions (figure 6).
2. Increases in photosynthetic rates by 20 to 60% (Cure, 1985).
3. Decreases in stomatal conductance and transpiration rates of approximately 16 and 33%, respectively (Cure, 1985).
4. Increased water use efficiency, but not necessarily a change in crop water use due to more leaf production (Baker et al, 1988; Cure, 1985).
5 However, further increases in CO2 concentrations may not have much impact on yields as rice apparently reaches a plateau in terms of photosynthetic acclimation (Baker et al, 1988).
Figure 6 indicates the range in estimated increases in rice yield with a doubling of CO2. Yield increases of 6 to 50% were found with an approximate doubling of CO2 to 660 ppm (U.S. DOE, 1989; Baker et al, 1988; Kimball, 1986; Cure, 1985). The Kimball and Cure estimates are based on earlier research under semi-controlled conditions. The Baker and DOE estimates are more recent and represent results from state-of-the-art experiments at Gainesville, Florida. However, the large range in increases of from 6 to 50% reported by the Gainesville group indicates the large amount of uncertainty present regarding the possible response of rice productivity to increasing CO2.
Other growth, physiological, and biochemical effects in response to enriched CO2 have been found in rice as other plant species (Strain and Cure, 1985). However, most of the experiments that determined these effects were not designed to test the potential impacts of global climate change.
Rice production can be dramatically affected by temperature. Traditionally, cool temperatures have been more limiting for rice production than warm temperatures. In this regard, production areas could expand with increasing temperature. However, rice plants also respond to high temperatures. Thus, for tropical areas, increased temperature by itself could lead to:
(a) Grain yield decreases above a critical temperature greater than 30deg. C (U S DOE, 1989).
(b) Increased plant growth rate and decreased growth duration leading to shorter grain filling period which varies from 25 days in the tropics to 35 days in the temperate zone (Swaminathan, 1984).
(c) Spikelet sterility (Yoshida and Parao, 1976), which becomes very severe near 40deg. resulting in complete loss of crop production.
(d) Increased respiration but minimal changes in photosynthesis across a broad optimum range in temperatures (Sato and Kim, 1980).
Effects of CO2 and temperature on the rice ecosystem
Indirect effects of global climate change on rice production will also occur via ecosystem responses (Barnes et al, 1989; Bazzaz et al, 1985; Oechel and Allen, 1985). Changes in weed competition, insect infestation, disease severity, nitrogen fixation by symbiotic organisms and other components of the ecosystem due to increased CO2 and temperature could severely impact rice production and offset any increases in yield due to the effects of global climate change on rice itself. However, the direction of these effects is unknown. Examples of the types of changes which may occur are:
1. Changed competitiveness could occur between rice which has the C-3 type of photosynthesis vs. barnyard grass (Echinochloa crus-galli world's worst rice weed) which exhibits C-4 photosynthesis as has been found for other crops (Patterson et al.1984)
2. Altered nitrogen fixation by the Azolla-Anabaena complex with increased CO2 and possibly temperature.
3. Altered insect and disease infestations due to enhanced growth rates with increasing temperature.
Interactive effects of CO2 and temperature on rice
The potential interactive effects of CO2 and temperature on rice are also critical for predicting the effects of global climate change on rice (Acock and Allen, 1985). There are few data on interactions, but preliminary experiments indicate that:
1. CO2 enrichment did not compensate for large reductions in rice yield due to increased temperature (U.S. DOE, 1989).
2. Complex interactions may occur for components of the rice ecosystem which may have profound effects on rice production, e.g., increased CO2 may overcome adverse high temperature effects on Azolla (Idso et al, 1989; Allen et al, 1988).
The results from the U.S. DOE (1989) report are particularly interesting. In one of the few CO2 and temperature studies, this preliminary information from the USDA/University of Florida indicates that increased temperatures result in large reductions in rice yield which were not compensated for by increases in CO2 (U.S. DOE, 1989). Yields with temperatures of 28/2l/25deg. C (daytime, nighttime, paddy), were 7.9 and 8.4 tons/ha for 330 and 600 ppm CO2, respectively; but with temperatures of 34/27/31deg.C were only 4.2 and 4.8 tons/ha for 300 and 660 ppm CO2. With temperatures of 40/33/27deg.C rice did not have any yield at either 330 or 600 ppm CO2. These experiments need to be corroborated by other research, but they indicate the potentially dramatic effects of CO2 and temperature on rice production.
Finally, while there is at least some information regarding the single effects of UV-B, CO2 and temperature on rice; the interactive effects of these factors are largely unknown despite the fact that in the real world they would be expected to change in concert. There have been no reported studies on the interactive effects of UV-B, CO2 and temperature. Interactive effects between enriched CO2 and increased temperature have been recognized as important in the prediction of global climate change impacts, but there have been few actual experiments where both factors have been controlled.
In addition, the indirect effects of global climate change could have even more dramatic effects on rice production. For example, altered timing and magnitude of precipitation can induce drought or flood injury (Sastry, 1976). Increased temperatures, and/or changes in precipitation could have dramatic impacts on rice diseases and insects. Enhanced UV-B, enriched CO2 and increased temperatures may all alter competition between rice and major weeds, and the contribution of other organisms to nitrogen fixation in rice fields.
The U.S. EPA traditionally has focussed on the control of single pollutants within the United States, however, the scope of the current environmental problems requires a global approach to pollution prevention. It is clear that an assessment of the agricultural effects of global environmental change must include rice as a crop of primary interest. Thus the U.S. EPA, in cooperation with the IRRI, has initiated a major program of research into the effects of global warming, global climatic changes, increases in atmospheric CO2, and increases in UV-B on rice production. Because most of the world's rice is grown and consumed in tropical Asia, this program will concentrate specifically on the likely effects in that region.
Adaptation to, or mitigation of the effects of UV-B and global climate change requires initiation now of forward looking research programs. The basic adaptation avenue for agricultural crops is through breeding (or biotech) programs such as those conducted at IRRI. These programs take time, and the proposed research will provide the framework to at least begin consideration of breeding resistance to UV-B and global climate change into rice. The primary mitigation avenue for crops is through alteration of management practices such as planting date, fertilization procedure, etc. However, before adaptation/mitigation studies can start fundamental data are needed on the extent and magnitude of UV-B and global climate effects on rice production.
The EPA/IRRI program on the effects of UV-B and global climate change on rice will address five issues critical to policy makers in the U.S. and tropical Asia.
I . What are the effects of UV-B and global climate change on the rice ecosystem?
2. How extensive and intensive will those effects be for Asia?
3. How important is the rice ecosystem as a source of greenhouse gas emissions (methane), and what are the impacts of UV-B and global climate change on those emissions?
4. What adaptation/mitigation options are available to reduce the impacts of UV-B and global climate change on rice yields?
5. What adaptation/mitigation options are available to reduce the magnitude of greenhouse gas emissions from the rice ecosystem?
Existing data are not adequate to answer the policy issues listed above, at either the rice plant, the rice ecosystem, or the risk assessment level of concern. The seven objectives listed below outline the research information required to provide the U.S. EPA and IRRI with the information needed to evaluate the effects of stratospheric ozone depletion and global climate change on the rice ecosystem. These objectives are:
I . To characterize the current and predicted levels of UV- B, CO2 and temperature in critical rice growing areas.
2. To determine the fundamental effects of UV-B radiation; and ultimately UV-B radiation interactions with CO2 and temperature on rice plants and the rice ecosystem.
3. To determine the fundamental effects of enriched CO2 interacting with elevated temperatures on rice plants and the rice ecosystem.
4. To determine the rates of methane emission from rice fields, and the impact of UV-B and global climate change on those emissions.
5. To develop, calibrate and validate models that incorporate the effects of UV-B and global climate change on: (a) rice plant productivity, and (b) rice ecosystem function.
6. To assess the risk to rice ecosystems from UV-B and global climate change through use of models and Geographic Information Systems (GIS).
7. To assess the adaptation and mitigation options for the rice ecosystem in response to global climate changes.
Breadth of the Study
Fulfillment of objectives will be a complex and lengthy task. As indicated earlier, little is currently known about the response of rice plants to UV-B radiation, enriched CO2, or elevated temperature. Even less is known about the responses of important rice ecosystem components (pests, pathogens, weeds, nitrogen fixers, methane producers) to these factors. To accurately determine the qualitative and quantitative nature of these effects will require a number of highly integrated experimental and modeling efforts, rigorous data quality control, and effective coordination of research activities between cooperating groups.
To facilitate integration of research activities, this program takes a modified cascading approach with each task building upon the results of other tasks, ultimately leading to mitigation options as shown in Figure 7. However, this does not mean that activities will be isolated sequentially in time. On the contrary, the activities will be initiated concurrently so that there will be a continual iterative process where results from one influence and feedback to other activities. For example, as experimental results on rice responses to climate change become available, they will immediately be fed into the modeling effort. The subsequent modeling outputs will then be used to design further experiments. The research tasks for this program fall into three groups: climate scoping, experimental, and assessment.
Atmospheric modeling studies as indicated by Task 1 in Figure 7 will produce plausible UV-B and climate change scenarios for the tropics. Atmospheric chemistry and radiative transport models will be used to produce estimates of UV-B levels in tropical rice producing areas. GCMs and current climatic data will be used to produce estimates of climatic conditions (temperature and possibly precipitation) in rice growing areas both at the current time and after a doubling of atmospheric CO2. The atmospheric modeling outputs will be evaluated in a GIS context. Preliminary estimates of increases in UV-B, CO2, and temperature also will be used to define treatment conditions for the fundamental experimental tasks.
The experimental studies will provide data to construct and to validate plant process and ecosystem models which will then be used for predictive purposes and regional impact assessments.
Experimental studies will be conducted on the sensitivity of rice, the dose-response relationships, and other responses to UV- B (Task 2), and global climate change (enriched CO2 and increased temperatures) (Task 3). The research will include greenhouse and controlled environment studies for initial assessments of the range in sensitivity to the stresses inherent among rice genotypes, and to explore specific mechanistic responses to provide new data for physiological process models. For example, gas exchange rates will be determined for rice plants exposed to enhanced UV-B on enriched CO2 . Field studies will be used to obtain yield data, to assess the responses under more realistic conditions, and to extend conclusions from controlled environment studies.
The important, though more indirect, influences of the environmental changes on the rice ecosystem will be examined under field and greenhouse conditions as well. These experiments will examine the effects of UV-B and global climate change on rice diseases such as Rice Blast, insects, weeds such as Barnyard Grass (Echinochloa crus-galli), and on nitrogen-fixing organisms such as planktonic algae and Azolla. For example, experiments will be conducted on the effects of UV-B on the susceptibility of rice plants to strains of rice blast fungus, on the parasitic fitness of the fungus, and on host pathogen interactions.
Additional studies will investigate current methane emission rates from rice fields and how those rates would change with enhanced UV-B and global climate change (Task 4). Variation in emission rates due to environmental factors and possibly management practices also will be studied. Methane studies will use field surveys to quantify current CH4, flux rates and dynamics, and experimental treatments will be used to determine the response of methanogenesis to UV-B and climate change treatments. The results from the methane studies will also be available for other researchers studying biogenic inputs into global climate models.
Simulation models will be developed to predict rice plant and ecosystem responses to UV-B and climatic change. Rice yields will be calculated for the site and extrapolated for other areas using both rice physiological and rice ecosystem models. The outputs from the ecosystem model will serve as inputs to the GIS spatial databases. These databases will then be used to produce the regional rice yield change estimates (Task 6). Ultimately assessments based on these estimates will provide options for policy makers and rice producers for recommendations to mitigate the effects of global climate changes on rice (Task 7).
Examples of the types of information which will be produced by the proposed assessments are given below based on preliminary modeling studies for rice producing areas of Asia. The estimates were made for a doubling of atmospheric CO2:
1. For southeastern China, the major rice producing area of the country, air temperatures would increase by 3-6deg.C (Gutowski et al, 1988). However, the impacts of the temperature rise on rice production in China were not determined.
2. For all of Japan, air temperatures should increase by 2-4deg.C and rice yields should increase by 9%, (Yoshino et al, 1988).
3. For the Chiang Mai area of Thailand, air temperatures would increase by about 3deg.C in July and rice yields would decrease by 7% with optimum growing practice including irrigation and fertilization (Panturat and Eddy, 1989)
However, except for possibly Japan, none of these three modeling efforts adequately represents the possible future yield of rice with global climatic change as they did not include the possible beneficial effects of CO2 on rice yields. Future assessments need to include both the impacts of CO2 and temperature on rice production, and to calculate those effects for critical regions of each rice producing country in Asia. In addition, a complete assessment will also include experiments on the effects of UV-B radiation on plants.
This program is intended to be adaptable and responsive to emerging policy needs and to new scientific information as it becomes available. As such, program evaluations are planned annually to review progress and, if necessary, implement mid-course corrections in research goals and direction.
Cooperation between IRRI and ERL-C
The objectives of this research program will be met through a cooperative effort between the U.S. EPA's ERL-C and IRRI. The ERL-C has considerable expertise in investigating UV-B effects on vegetation, ecosystem modeling, use of geographic information systems, and in preparing integrated assessments of environmental effects from pollutants in order to provide information for governmental regulations and decision making purposes. The IRRI has unique capabilities to conduct field and controlled environment research on rice, as well as on rice pests and soils. IRRI also has many international cooperators who will provide additional expertise for their research.
Because the goal of this program is both complex and ambitious, it will be essential to seek the advice, guidance, and assistance of international experts in the areas of concern to the program. To that end, the program is designed to foster cooperation of experts in three ways:
I . A Research Management Committee (RMC) will be formed for continual coordination of research activities at IRRI and ERL-C. The RMC will be composed of two co-chairpersons (one representing EPA and one from IRRI), plus the Principal Investigators from various research activities. The RMC will hold an annual project planning Meeting.
2. Annual comprehensive scientific reviews of the research program (involving all the principal investigators) will be conducted. An independent peer review will assess the progress, current research, and future research plans. The peer review will provide the results of their review to the co-chairmen of the RMC who are responsible for its distribution. ERL-C in conjunction with IRRI will select the peer review panel and conduct the review. Senior project staff from the visiting group as well as all project staff from the host group will attend. The annual project planning meeting and peer review will alternate between EPA and IRRI.
3. Scientific advisory groups may be necessary to provide the advice and guidance on specific experimental issues or to assist in defining critical research paths and determining important scientific questions and experimental approaches. These will include nationally and internationally recognized experts nominated by IRRI and/or EPA.
This project will focus only on effects of UV-B and C02/temperature on rice. Research on interactions between these factors and other stresses such as water stress or tropospheric ozone is being conducted by other research groups. Contacts and coordination with these groups will be made so that their findings can be used with the rice research.
This research will provide the US EPA Office of Air and Radiation and IRRI with information needed to assess the terrestrial effects of stratospheric ozone depletion and global climate change on the world's most important crop, rice. The information will consist of:
1. Projections of changes in rice yield for Asia with different UV-B and global climate change scenarios.
2. Empirical data on the response functions for rice and rice ecosystem components associated with UV-B radiation, atmospheric CO2, and temperature.
3. A process-based model for rice plants modified for UV-B and global climate change inputs .
4. A rice-ecosystem model.
5. Outputs from UV-B and global climate change models regionalized for Asia.
6. GIS databases for critical factors affecting crop production in Asia.
7. Empirical data for methanogenesis from rice fields with different climate change scenarios.
8. Assessment documents containing information on adaptation and mitigation options available to reduce impacts of UV-B and global climate change on the rice ecosystem.
Finally, if rice production is at risk from UV-B due to stratospheric ozone depletion, or from global climate change; it will be critical to identify and assess possible strategies for mitigating the impacts, or adapting to the effects, without net losses in rice production or ecosystem stability. Certainly with the limited data currently available, it is premature to recommend specific mitigation options. However, the identification and evaluation of such options is a major goal of the EPA's rice research program, and will be an integral part of the findings of the program. Although it is uncertain at present what mitigation strategies will be identified, two areas offer promise:
1. Selection of rice cultivars that are resistant to UV-B and global climate change insult. Rice exhibits wide cultivar variability in UV-B and temperature responses. Currently available resistant cultivars may, in some cases, serve to replace more sensitive cultivars in farmers fields. Resistant cultivars may also be used by rice breeders to select and develop new cultivars that combine other favorable trails with UV-B resistance and adaptability to climate change.
2. Use of rice management practices to reduce UV-B and high temperature exposure, and minimize the impacts on these stresses on rice and critical ecosystem components. Although less well-defined than the first area, certain management practices may be useful to mitigate the impacts. For example, the timing of planting may be shifted so sensitive growth stages avoid times of high UV-B exposure, or water and agricultural chemical management practices may be altered to reduce indirect effects of UV-B and global climate change on the rice ecosystem. Other possibilities will be explored as part of the research program.
The information in this document has been funded wholly or in part by the U.S. Environmental Protection Agency. It has been subject to the agency's peer and administrative review, and it has been approved for publication as an EPA document.
The authors wish to acknowledge the following scientists who are contributing to the research described in this plan; at ERL-C, Dr. D. Bachelet, Dr. P. Barnes, Mr. D. Brown, Mr. S. Holman, Ms. S. Maggard, Dr. D. Tingey, and Ms. C. Wise; and at IRRI, Dr. M. Bonman, Dr. F.W.T. Penning de Vries, Dr. K. Heong, Dr. H. U. Neue, Ben Vergara and H. Zandstra. We would also like to thank Drs. M. Bonman and B. Vergara for preliminary information from their UV-B, rice, and rice blast studies.
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