Location: Plant Science Research2011 Annual Report
1a. Objectives (from AD-416)
1. Assess and parameterize for models, the effects of changing temperature, vapor pressure, atmospheric carbon dioxide and ozone on crop performance. (Booker, Fiscus, Burkey) 1.A. Design and construct an air exclusion system for treating crops with elevated ozone, elevated temperature and elevated atmospheric carbon dioxide concentrations. 1.B. Assess and parameterize for crop growth models (DSSAT-CSM -CROPGRO-Soybean and DSSAT-CSM-CERES-Wheat), the effects of elevated ozone, temperature and carbon dioxide on soybean and wheat physiology, above and belowground growth and development, yield and seed quality. 1.C. Characterize interactive effects of temperature, vapor pressure, carbon dioxide and ozone on plant growth in outdoor controlled environment systems. 2. Characterize the effects of the major climate change variables temperature, atmospheric vapor pressure, carbon dioxide, ozone and possible interactions on the infection rates and progression of the disease in plants infected with wheat rust. (Fiscus) 3. Identify soybean germplasm that will contribute to development of stress tolerant cultivars. (Burkey, Booker) 3.A. Identify soybean cultivars with enhanced ozone tolerance. 3.B. Characterize the inheritance of ozone tolerance in soybean ancestors. 4. Identify the mechanisms through which soil microorganisms mediate perennial grasses, forage legumes and ecosystem responses to changing climate conditions. Develop economically sustainable production systems for forage and biomass crops that reduce the net emissions of greenhouse gases per unit of forage or biomass production. The research will contribute to the ARS GRACEnet project.
1b. Approach (from AD-416)
Experiments will be conducted in available open top field chambers, greenhouse exposure chambers, and custom Outdoor Plant Environment Chambers (OPECs) or in a new air exclusion system to be developed by this project that allow for testing of plant responses to combinations of carbon dioxide and ozone under contrasting conditions of temperature and vapor pressure deficit. A multi-year field study will be established using the air exclusion system to test the effects of elevated ozone, temperature and carbon dioxide on a soybean-winter wheat continuous no-till cropping system. Detailed assessments of plant growth, biomass, and yield along with measurements of leaf gas exchange, tissue chemistry and micrometeorological data will be used as inputs for parameterization of DSSAT-CSM CROPGRO-Soybean and CERES-Wheat models. Ozone-sensitive and tolerant snap beans will be grown in the OPECs where control of relative humidity and temperature allows for the study of plant responses to elevated ozone and carbon dioxide under contrasting vapor pressure deficit conditions. Wheat cultivars that are susceptible and resistant to stripe or stem rust will be grown in the OPECs and inoculated with pathogens under a range of carbon dioxide, ozone, temperature and vapor pressure deficit conditions to examine the potential impact of these climate change factors on infection and progression of disease. Soybean germplasm will be exposed to elevated ozone conditions in greenhouse exposure chambers or open-top field chambers and foliar injury and seed yield measurements used to identify tolerant cultivars. Single nucleotide polymorphism markers will be applied to a soybean population developed from a cross between ozone-sensitive and tolerant soybean ancestors and the population screened for ozone-induced foliar injury in the greenhouse. Marker and phenotype data will be combined to develop a map of soybean ozone-tolerance genes.
3. Progress Report
A prototype Air Enrichment System (AES) was designed and built that provides a clean-air (charcoal-filtered) environment along with elevated temperature, ozone and carbon dioxide (CO2) treatment capabilities. AES uses passive solar heating and electrical resistance heaters to elevate the air temperature 2.2 ± 0.4 °C and adds moisture to maintain relative humidity. AES meets the Performance Specifications for temperature, humidity, air quality and light established for this project. Two prototype AES along with two control units and ambient plots were planted with soybean in June. Harvest and environmental data are being summarized for use in a crop growth computer model. Drought stress studies are difficult because of the unpredictability of rainfall events. We developed the "water stress field", a form of precipitation exclusion technology, for the multiple purposes of studying the physiology of water stress, comparing genetic lines for desirable water stress characteristics and to examine the interactions between soil moisture levels and the toxic effects of ambient atmospheric ozone. The 2008 and 2009 data were used to develop a model for soybean predicting leaf conductance from measurements of soil volumetric water content in the profile down to 40 cm. Coupled with ambient ozone measurements a flux based risk assessment model, based on soil moisture is also being developed. Five wheat varieties with different levels of susceptibility/resistance to the wheat stripe rust pathogen, Puccinia striiformis, were vernalized and grown under combinations of elevated CO2, ozone, and atmospheric vapor pressure deficit. Ozone significantly damaged the growth and seed production of all five varieties. CO2 promoted growth and lessened the effects of ozone. Vapor pressure deficits were too low to allow for rust development in the leaves. A second experiment in open-top chambers, 60 varieties of wheat, barley, and oat juvenile plants were shown to vary widely in response to ozone exposure, with oat and barley varieties exhibiting greater leaf discoloration than wheat. Open-top chamber studies were initiated to test the feasibility of identifying ozone-tolerant soybean cultivars based on pedigree analysis. Two ozone-tolerant soybean ancestors, two cultivars genetically related to the tolerant ancestors, and two ozone-sensitive ancestors are being compared using season long exposures to four different ozone concentrations ranging from sub-ambient to twice current ambient levels. Ozone responses are being evaluated in terms of foliar injury, seed yield, and antioxidant metabolism. Final steps were completed in the development of a soybean population to map stress tolerance genes for drought, iron deficiency chlorosis, ozone, salt, and toxic soil aluminum. The mapping population consists of 240 random inbred lines developed from a cross between Fiskeby III and Mandarin Ottawa plant introductions. Seed increases were completed and initial screening of the population for ozone, drought and iron deficiency chlorosis begun. DNA for use in marker aassays was extracted from leaf tissue for approximately 90% of the random inbred lines.
1. Soil microbial responses to elevated carbon dioxide and ozone in a wheat-soybean cropping system. Climate change factors such as rising atmospheric carbon dioxide (CO2) and ozone can exert significant impacts on crop growth, but it remains largely unexplored how the soil microbes in agricultural systems respond to these factors. This severely hinders our ability to predict soil carbon sequestration potential. Using a long-term field study conducted in a no-till wheat-soybean rotation system with open-top chambers, ARS researchers in Raleigh, NC, showed that elevated CO2 stimulated plant biomass production and ozone lowered it, but only elevated CO2 significantly affected soil microbial biomass, respiration and community composition. Enhancement of microbial biomass and activities by elevated CO2 coincided with increased soil nitrogen availability, likely due to stimulation of soybean nitrogen-fixation under elevated CO2. These results highlight the need to consider the interactive effects of carbon and nitrogen availability on microbial activities when projecting soil carbon balance under future CO2 scenarios. The addition of nitrogen to agricultural systems through fertilizers or legume crops may stimulate microbial decomposition processes and limit carbon sequestration potential. Our results also suggest that projected ozone concentrations under future climate scenarios may reduce plant productivity but have limited impact on soil microbial processes.
Cheng, L., Booker, F.L., Burkey, K.O., Tu, C., Shew, H.D., Rufty, T., Fiscus, E.L., Hu, S. 2011. Soil microbial responses to elevated CO2 and O3 in a nitrogen-aggrading agroecosystem. PLoS One. 6:e21377.