2007 Annual Report 1a.Objectives (from AD-416) Quantify the combined effects of elevated carbon dioxide and ozone concentrations on soil carbon dynamics in a soybean-wheat field crop system; quantify the effects of temperature on the physiology, biomass production and seed yield of selected crop plants under conditions of elevated carbon dioxide and ozone; and identify soybean germplasm with enhanced growth and yield potential under elevated levels of carbon dioxide and ozone, and determine the underlying mechanisms and associated genes that control plant responses to these gases. Application of results from this research in models and decision support systems will ultimately support management strategies that optimize sequestration of carbon in agricultural soils to offset carbon dioxide emissions. Research results should also aid in the development of crops that tolerate ozone and utilize carbon dioxide more effectively. 1b.Approach (from AD-416) Research will be conducted using field and greenhouse chambers for control of ozone and carbon dioxide concentrations and temperature. Effects on yield, development, and quality for specific crops (e.g. soybean, snap bean, wheat and selected forages) and on changes in soil carbon will be tested. To evaluate the interactive effects of ozone, carbon dioxide, and temperature on plants, studies will include measurements of leaf conductance, photosynthesis, chlorophyll fluorescence, carbon metabolism, and biochemical systems that detoxify reactive oxygen intermediates formed from ozone. To evaluate the effects on agricultural soils, studies of plant response to ozone and carbon dioxide will be accompanied by measurements of soil microbial biomass, microbial community structure, and microbial activity, soil carbon distribution among carbon pools, soil carbon turnover using delta 13C mass spectrometry, and nitrogen mineralization. Genetic variability of response to ozone and carbon dioxide will be assessed through a combination of screening and pedigree analysis. Development and testing of Arabidopsis mutants will be conducted to identify genes associated with plant response to ozone. 3.Progress Report The second year of a two crop (soybean-wheat) no-till experiment was completed. This experiment is designed to investigate long-term effects of elevated ozone and carbon dioxide on plant-soil interactions and soil C dynamics. Elevated carbon dioxide increased aboveground biomass and seed yield, but added ozone had no significant effect on these parameters. Photographs obtained through clear plastic tubes in the ground showed that elevated CO2 strongly stimulated, while ozone suppressed, soybean and wheat root growth. Relatively low ambient ozone concentrations and extended drought conditions in 2006 likely reduced the impact of ozone on growth and yield. It appeared that improved plant-water status at elevated CO2 increased relative yield production over the previous year (25% versus 10%), although cultivars differed between 2005 and 2006. The effect of water stress on biomass, yield and soil C sequestration in 2006 is being tested in 2007 by growing plants under well-watered conditions. Elevated CO2 treatments have resulted in 27% more post-harvest plant residues added to the soil surface while 15% less residue material has been added in the elevated ozone treatment compared with clean-air controls. However, no consistent treatment effects have been observed for soil microbial biomass carbon and nitrogen, extractable nitrogen, nitrogen mineralization and soil respiration. Stable isotope analysis of soil fractions showed that C from the elevated CO2 treatments was entering the soil C cycle, but %C in the soil was unchanged among treatments. Some of these results were anticipated because it is known that soil C levels are slow to respond to conversion to no-till practices, but influences of elevated CO2 and ozone in such a system have not been previously tested. It may be that gas treatment effects are also slow to impact soil C and N dynamics. Screening of soybean ancestors for ozone-induced foliar injury under greenhouse conditions appeared to be a good predictor of ozone injury in open-top chamber field experiments. However, foliar injury was not always a good predictor of seed yield loss. Open-top chamber studies were conducted with selected soybean ancestors where plants were exposed to season long treatments of low ozone (22-25 ppb 2-hour seasonal mean) or elevated ozone (63-77 ppb seasonal 12-hour mean). Specific ancestors exhibited low foliar injury with 25-30% yield loss whereas others were extensively injured with only 10% yield loss. Ozone effects on yield components were complex and included combinations of reduced seed size (suggesting ozone impact on general plant metabolism such as photosynthesis, translocation, etc.) and reduced pod/seed number (suggesting direct impact of ozone on reproductive processes such as flowering, pollen viability, etc.). One implication of these results is that development of ozone tolerant germplasm based on foliar injury alone may not take into account the full range of ozone effects. 4.Accomplishments Title: Changes in Atmospheric Vapor Pressure Deficit Caused by Increased Global Temperatures May Affect the Susceptibility of Plants to Ozone Damage Prediction of impacts of global climate change and the interactions of environmental pollutants on plant growth is still not resolved due to a number of confounding interactions in the response to environmental variables such as temperature and atmospheric vapor pressure deficit (vpd). We examined the interactive influence of vpd and temperature on the long term growth of tall fescue, a cool season grass. At a constant vpd, contrary to expectations, the growth of this grass markedly increased with temperature. Increasing vpd at constant temperature, which is a common consequence of most temperature-increase experiments, actually caused growth to decrease. Assuming vpd remains constant with global warming as it has in the past then growth of cool season species might actually be stimulated by temperature increases. These results also suggest the importance of possible changes in vpd in determining the susceptibility of plants to pollutant ozone. NP203 Component IV Ozone Impacts, Problem Statement – Mechanisms of Ozone Response 5.Significant Activities that Support Special Target Populations NONE 6.Technology Transfer Number of web sites managed 2 Number of non-peer reviewed presentations and proceedings 5 Number of newspaper articles and other presentations for non-science audiences 3 Review Publications Chen, X., Tu, C., Burton, M., Watson, D., Burkey, K.O., Hu, S. 2007. Plant nitrogen acquisition and interactions under elevated CO2- impact of endophytes and mycorrhizae. Global Change Biology. 13:1238-1249. Booker, F.L., Burkey, K.O., Pursley, W.A. 2007. Elevated carbon dioxide and ozone effects in peanut. I. Gas-exchange, biomass, and leaf chemistry. Crop Science. 47:1475-1487. Burkey, K.O., Booker, F.L., Pursley, W.A., Heagle, A.S. 2007. Elevated carbon dioxide and ozone effects on peanut. II. Seed yield and quality. Crop Science. 47:1488-1497.