Location: Plant Science Research2012 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:
Improvements were made in our Air Enrichment System (AES), an exposure system designed to provide a clean-air (charcoal-filtered) environment along with elevated temperature, ozone and CO2 treatment capabilities. The prototype AES combined passive solar heating and electrical resistance heaters to elevate average air temperature by 2°C while adding moisture to maintain relative humidity. To further increase temperature in heated plots, modifications being incorporated include new panel perforation patterns that direct heated air lower in the plots, increased volume of the passive solar heating units, and the addition of a water-to-air solar heat exchange system. All modifications were based on preliminary testing. Two modified AES heated plots along with two control units and ambient plots were planted with soybean in June. Harvest and environmental data are being collected for use in a crop growth computer model. Two wheat varieties with different levels of susceptibility/resistance to the wheat stripe rust pathogen, Puccinia striiformis, were vernalized and grown under combinations of elevated carbon dioxide and ozone in our outdoor plant environment chambers. Optimizing day-night temperature and the increasing relative humidity provided the conditions necessary for pathogen infection and development on plants. Effects on foliar symptoms, biomass, and seed yield are being assessed to evaluate the potential impact of climate change factors on plant-pathogen interactions. Open-top chambers were employed to test the potential for identifying ozone-tolerant soybean cultivars on the basis of pedigree analysis. Two ozone-tolerant soybean ancestors (Fiskeby III and Fiskeby 840-7-3), two modern cultivars genetically related to these tolerant ancestors (Maple Ridge and Maple Amber), and an ozone-sensitive ancestor (Mandarin Ottawa) were compared using season long exposures to four different ozone concentrations ranging from sub-ambient to twice current ambient levels. Seed yield of Fiskeby III was not reduced under any ozone treatment employed, Fiskeby 840-7-3 yield was reduced at high ozone concentrations, and Mandarin Ottawa yields declined as severity of the ozone treatment increased. Cultivars derived from one of the ozone-tolerant parents did not consistently exhibit the parental ozone response, suggesting that pedigree analysis must be combined with direct screening of germplasm to effectively evaluate the ozone tolerance. A mapping population of 240 random inbred lines has been developed from a cross between Fiskeby III (ozone-tolerant) and Mandarin Ottawa (ozone-sensitive) genotypes. DNA was extracted from root tips of the random inbred lines and both parents. Assay of single-nucleotide polymorphism (SNP) DNA markers was completed to provide data for constructing the linkage map. The screening of the population for ozone response was completed using greenhouse exposure chambers with the Fiskeby III and Mandarin Ottawa parents serving as checks. The population exhibited a wide range of foliar injury in response to the ozone treatment. Assessment of the phenotype data has begun in preparation for mapping ozone response genes in soybean.
1. G-proteins have minimal effect on plant response to ozone stress. Development of ozone tolerant plants is one approach to alleviate the adverse effects air pollution on agricultural crops. Progress requires knowledge of the critical points in plant metabolism that can be manipulated through genetic approaches to enhance ozone stress tolerance. ARS researchers at Raleigh, North Carolina and collaborators at the University of North Carolina-Chapel Hill found that genetic silencing of G-protein genes in the model plant, Arabidopsis thaliana, had had little effect on many processes commonly associated with plant response to ozone stress. This suggests that the G-protein signaling pathway is not a significant target for altering ozone tolerance. Future research to enhance ozone tolerance of crops should be directed toward other aspects of metabolism.
2. Re-evaluation of antioxidants in plant defense against ozone stress. Knowledge of the critical points in plant metabolism that can be manipulated to enhance stress tolerance is required for development of new cultivars adapted to climate change. For several decades, ascorbic acid (vitamin C) in the cell walls of plant leaves was considered a first line of defense against ozone stress with protection thought to be provided by ascorbic acid reacting directly with ozone to prevent ozone damage. ARS researchers at Raleigh, North Carolina and collaborators at the University of North Carolina-Chapel Hill found that leaf cell walls of Arabidopsis thaliana contain ascorbic acid as well as phenolic compounds identified during this study, but modeling the ozone scavenging capacity of these molecules indicated that direct reaction with ozone was not a significant protection mechanism. These antioxidant compounds may play a role in protecting plants from ozone stress, but do so as part of a more complex mechanism to be defined through future research.
3. Atmospheric vapor pressure deficit is a key factor in plant response to ozone stress. Accurate prediction of impacts of global climate change and atmospheric pollutants on plant growth is complicated due to interactions with environmental variables such as atmospheric vapour pressure deficit (vpd). ARS researchers at Raleigh, North Carolina showed that ozone-induced reductions in snap bean growth and yield under low vpd (high humidity) did not occur under high vpd (low humidity), although overall yield potential was also limited by high vpd conditions. These results suggest that efforts to model climate change impacts on vegetation must consider interacting environmental factors and that vpd is a critical factor to consider when predicting the effects of ozone air pollution.
4. Field testing of a snap bean ozone bio-indicator system. Predicting ambient ozone impacts on crops for a specific location and growing season is difficult because plant response is dependent on multiple factors including those unique to the local environment. Direct measurement of effects is impractical for most situations due to the lack of a “clean air control” necessary for quantifying impacts. Bio-indicator plants provide one approach to circumvent some of these challenges. ARS researchers at Raleigh, North Carolina previously developed a snap bean bio-indicator system based random inbred lines that exhibit differences in ozone sensitivity. In collaboration with ARS colleagues at Urbana-Champaign, Illinois, these snap bean lines were grown under ambient and elevated ozone using the free air concentration technology available at the SoyFACE experimental site. Ratios of sensitive to tolerant genotype pod yields were identified as a useful measurement for assessing ozone impacts. The results suggest that this snap bean system could be used to quantify ozone effects in specific locations with potential applications in diverse environments including agricultural fields.
5. Ozone air pollution reduces forage quality. Ozone impacts on plant growth and yield are well documented for multiple crop species, but less is known about ozone effects on the quality of agricultural products. Researchers at Auburn University in collaboration with ARS researchers in Raleigh, North Carolina exposed a mixture of common Southern Piedmont grassland species to elevated ozone and fed the forage to rabbits in a digestibility experiment. Forage grown under elevated ozone resulted in decreased digestible dry matter intake. These findings suggest that ozone air pollution can have a negative impact on forge quality, resulting in decreased nutrient utilization by mammalian herbivores.
6. Fine-root classes are a collection of discrete diameter groupings. Root systems are routinely photographed as an image of the whole root system. This is like looking at the whole forest to investigate the relationship of several trees. ARS researchers at Raleigh, North Carolina took a series of small images of a whole perennial ryegrass root system and analyzed each separately. They found that the smaller roots could be classified by discrete diameter groupings rather than the previously thought random collection of diameters. By using this procedure, scientists will be able to document the differential response of different root diameter classes to environmental perturbations and then select plant material that will better tolerate environmental stresses.
7. Mid-Appalachia small farmers contend with unusual soil problem. Productivity in mid-Appalachian soils is limited by high levels of aluminum, low pH, and inaccessible phosphorus. ARS researchers now at Raleigh, North Carolina reviewed the research on low pH soils and high aluminum throughout the Appalachian mountain region. They concluded that although topical treatments of liming agents (to raise soil pH and reduce the availability of aluminum) were effective both north and south of the mid-Appalachian region, liming was not effective on the central Appalachian soils. This conclusion was based on 20 years of research that demonstrated that only in this region did liming treatments not disperse into the deeper layers of soil. The basis for this phenomenon remains unknown. Further research is required to identify this unusual soil problem and develop novel management practices to address the associated negative impact on productivity faced by small farmers in the region.
8. Soil surface condition improved with tall fescue management on eroded soil. How grasslands are managed for optimum restoration of soil quality is an open question needing scientific support. Scientists with the USDA Agricultural Research Service in Watkinsville, Georgia and Beltsville, Maryland collaborated to conduct an 8-year-long investigation of how tall fescue pastures could be managed to reduce soil compaction and improve soil organic matter accumulation. Soil bulk density (the scientific measure of soil compaction) declined with time under all pasture management systems, but more so with broiler litter fertilization than with inorganic fertilization, possibly due to the organic amendment that helped loosen surface soil by encouraging soil animal activity and/or by promoting greater root development. Soil organic carbon and nitrogen accumulated with time under all pasture management systems, but more so under grazed than under hayed management, likely due how the forage was harvested as cattle consumed forage on the pasture, but returned a large portion of the carbon and nitrogen back to the pasture via feces. No differences were detected in soil organic matter among tall fescue-endophyte associations (wild, novel, and free), nor between nutrient sources applied to fertilize pastures (inorganic and broiler litter). The results of this research have important implications for assessing soil quality of grazing lands in the eastern USA, but also for assessing the impacts of agricultural management on the potential to mitigate greenhouse gases, such as carbon dioxide.
9. Perennial pastures provide significant potential to sequester carbon in soil. Pastures are common in the eastern USA, but research documenting how pasture management affects soil organic carbon sequestration is limited. Scientists with the USDA Agricultural Research Service in Watkinsville, Georgia; Coshocton, Ohio; Brooksville, Florida; Ames, Iowa; and Temple, Texas reviewed relevant literature and synthesized information into a recommendation for program development to better estimate soil organic carbon sequestration. Pastures are capable of large soil carbon storage potential; greater than cropland and equal to forested land. Moderate grazing and amendment with animal manures are beneficial to soil carbon sequestration. Significant research gaps were identified in understanding the effects of how a diversity of forage management systems might impact soil organic carbon. This review will be particularly valuable to pasture managers, industry consultants, carbon trading representatives, and government policy advisors.
10. Rediscovering well-managed grazing systems for conservation. Ecologically sound grazing management is an under-used and under-appreciated conservation tool in the eastern U.S. Scientists from USDA Agricultural Research Service in Raleigh, North Carolina and Mandan, North Dakota collaborated with professional agricultural specialists with the Wisconsin Department of Agriculture, Trade, and Consumer Protection; Winrock International; Michael Fields Agricultural Institute; and USDA Natural Resources Conservation Service to prepare a perspective article that (a) summarized the potential of well-managed pasture systems to provide ecosystem services, (b) discussed the barriers to adoption of well-managed pasture systems, and (c) proposed potential solutions to move well-managed pasture systems forward through education and extension efforts. This perspective has broad implications for how agriculture might be practiced throughout the eastern U.S., especially through ecologically sound pasture-based management.
Booker, F.L., Burkey, K.O., Morgan, P.B., Fiscus, E.L., Jones, A. 2012. Minimal influence of G-protein null mutations on ozone-induced changes in gene expression, foliar injury, gas-exchange and peroxidase activity in Arabidopsis thaliana L. Plant Cell and Environment. 35:668-681.