Location: Plant Science Research2013 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:
Additional 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 treatments in field plots. The original passive solar heating units were replaced with additional water-to-air solar heat exchangers so that each heated plot now has a total of four heat exchangers in addition to the electrical resistance heating system. Experience to date suggests that the current design will provide an elevated temperature treatment of 3.5 to 4.5 degrees Celsius above ambient conditions. Replacement of the passive solar units significantly reduced the “foot print” of each plot so that the field can now accommodate additional experimental plots. AES heated plots are being compared with AES controls and ambient air plots in a replicated soybean study in 2013. The irrigation approach will target common soil moisture content across all plots, replacing simulated uniform rainfall events, to compensate for greater water usage in heated plots and reduce confounding effects of temperature and drought. Harvest and environmental data are being collected for use in a crop growth computer model. Four wheat varieties with different levels of susceptibility/resistance to wheat leaf rust, Puccinia triticina, were vernalized and grown under combinations of elevated carbon dioxide and ozone in our outdoor plant environment chambers. Optimized temperature and relative humidity conditions provided conditions to facilitate pathogen infection and development on plants. Disease latency and intensity, foliar symptoms caused by both ozone and pathogen infection, biomass, seed yield and seed quality were measured. Preliminary assessment of the data suggests there are significant interactions between genotype, gas treatment, and pathogen infection. Mapping ozone tolerance genes in soybean was advanced for a population of 240 recombinant inbred lines derived from a cross between Fiskeby III (ozone-tolerant) and Mandarin Ottawa (ozone-sensitive) genotypes. Single nucleotide polymorphism DNA markers were used to construct the linkage map. Data from screening of the population for ozone-induced foliar injury were finalized and formatted for quantitative trait loci (QTL) analysis. Mapping software was used to identify QTLs for ozone response on chromosomes 1 and 18. A project SY took an active role in leading an agroforestry experiment at the Center for Environmental Farming Systems in Goldsboro, NC. The experiment was established in 2007 and has a factorial design of three tree species (Pinus palustris, Pinus taeda, and Quercus pagoda) and two alley widths (12 and 24 m) with five replications. New research efforts were initiated, including (a) managing the integrated crop-animal component of the Farming Systems Research Unit in Goldsboro, NC and (b) collaborating in an on-farm research and demonstration effort with Cotton Incorporated and North Carolina State University to test cover crop impacts in cotton production on soil organic matter accumulation and alleviation of soil compaction.
1. Conservation management of cotton improves soil carbon sequestration throughout the Cotton Belt. Soil organic carbon sequestration can be a significant driver of how conservation management systems are adopted by producers and promoted by government agencies. Modeling of various tillage, crop rotation, and cover cropping conditions across the cotton growing region of the southeastern USA would allow us to assess the relative importance of soil type, climatic conditions, and management on soil organic carbon sequestration potential in the region. Scientists from USDA-ARS in Raleigh, NC and USDA-NRCS in Temple, Texas and Washington, DC estimated potential soil organic carbon sequestration under conventional and conservation management of cotton cropping systems in each county throughout the Cotton Belt using the recently calibrated soil conditioning index. Soil organic carbon was predicted to decline with conventional tillage in most regions of the Cotton Belt, except the Desert Southwest region. Any decision to continue farming with conventional tillage is also risky for soil loss from erosion on all but the flattest parcels of land. Soil organic carbon was predicted to increase (modestly to significantly) using a variety of crop sequences with no-tillage management, while adding winter cover crops to the crop sequence was beneficial to organic matter input and subsequent estimation of soil organic carbon sequestration in all regions of the Cotton Belt. Simulations were most sensitive to management and slope variations and much less affected by climate and soil textural variations. These results have important implications for the sustainable management of the 4.2 Mha of cotton land in the southern USA.
2. Simple soil carbon models effective at identifying nationally relevant conservation management approaches. Rapid and reliable assessments of the potential of various agricultural management systems to sequester soil organic carbon are needed to promote conservation and help mitigate greenhouse gas emissions. A collaborative effort was undertaken by scientists with the USDA-Natural Resources Conservation Service in Greensboro, NC and Lincoln, NC and the USDA-Agricultural Research Service in Raleigh, NC to assess the applicability across a wide range of environmental conditions throughout the United States (18 locations in AL, AZ, CA, CO, GA, IN, KS, NC, NM, OK, OR, PA, TX, WI, and WY) of two relatively simple soil carbon models [the carbon management assessment tool for voluntary reporting of greenhouse gases (COMET-VR) and the soil conditioning index (SCI)]. Models were consistent with each other in predicting changes in soil organic carbon due to a gradient in soil disturbance with tillage (i.e. lowest values with conventional tillage, medium values with minimum tillage, and highest values with no tillage). When variations in soil texture and crop rotation were considered, models produced different outputs in soil organic carbon trends. Although some differences in soil organic carbon predictions occurred between models, overall there was a strong correlation in results across the diversity of locations that could be adjusted through a gradient in environmental characteristics, such as mean annual temperature and precipitation. These results will have important implications for farmers, crop advisors, scientists, and policy makers interested in carbon trading schemes throughout the 330 million acres of cropland in the USA.
3. Mycorrhizal fungi limit carbon sequestration in soils under elevated atmospheric carbon dioxide. Arbuscular mycorrhizal fungi (AMF) are soil microbes that form a mutually beneficial relationship with the roots of about 80 percent of plants that grow on land. AMF help sequester carbon in soil by promoting soil aggregation that slows decomposition of organic matter. It is often assumed that this process will contribute to carbon sequestration in future atmospheres with elevated carbon dioxide. However, research conducted by scientists from the USDA-Agricultural Research Service and North Carolina State University in Raleigh, NC suggested this may not be the case. Greenhouse and field experiments showed that elevated carbon dioxide stimulates soil decomposition through a complex process to provide plants with reduced nitrogen required for growth under elevated carbon dioxide conditions. AMF mediate this process by stimulating soil microbes to break down organic matter and convert organic nitrogen into ammonia that becomes available to the plant. Carbon dioxide from organic matter is released into the atmosphere as a consequence. The results suggest that the capacity of soils to sequester carbon may be limited as atmospheric carbon dioxide rises. It may be possible to circumvent this limitation with technologies to control soil nitrogen transformations in favor of ammonia. This discovery suggests there is a need to re-evaluate the concepts behind predicting carbon budgets under climate scenarios with elevated carbon dioxide.
4. Surface soil organic matter is important for water infiltration in grazed pastures. Surface-soil characteristics are of particular importance in determining the environmental quality of a location, but also for determining the environmental quality of neighboring ecosystems, if considerable erosion, runoff, and gaseous emissions were to occur. Scientists at the USDA-Agricultural Research Service in Watkinsville GA and Raleigh NC evaluated water infiltration and penetration resistance (measures of surface soil compaction) and rainfall/runoff relationships during a 12-year pasture experiment that was differentiated by (1) source of nutrients (inorganic versus organic) and (2) how forage was utilized (unharvested, hayed, or grazed by cattle). Soil was denser immediately below the soil surface under grazed pastures, which caused higher penetration resistance and lower water infiltration than unharvested grass. However, greater accumulation of surface residue and soil organic carbon under grazed pastures compared with hayed management led to similar water infiltration, despite firmer soil when grazed. Runoff predominately occurred with a small percentage (15%) of rainfall events that exceeded the soils’ capacity to allow entry of water. These data suggest that well-managed pastures have high capacity to cycle water through soil, despite evidence of some soil compaction. This is because accumulation of surface residue and soil organic carbon are able to mitigate much of the negative effects of animal trampling on soil hydrologic conditions by creating a biologically active surface soil. Cattle grazing of mixed bermudagrass / tall fescue pastures can be considered a viable strategy to rehabilitate millions of acres of degraded cropland in the southeastern USA.
5. Stratification ratio of active soil carbon fractions were best indicators of soil quality improvement with conservation tillage in a semi-arid climate. Assessing soil quality of a diversity of soils around the world is complicated due to unique characteristics that pose challenges when using standard analytical techniques. Collaboration among scientists at the Spanish National Research Council (IRNAS-CSIC), University of Cordoba, and USDA Agricultural Research Service in Watkinsville, Georgia was undertaken to evaluate long-term changes in soil quality of a Vertisol in Spain using a relatively new concept of stratification ratio of soil organic matter fractions. Soil organic matter fractions were enhanced in the surface layer under no tillage, more so than in the surface layer under conventional tillage. Stratification ratio of ß-glucosidase activity was the most sensitive soil property to long-term effects of management. Low stratification ratios were observed relative to ratios from other soils around the world, which may have been due to the self-tilling properties of the high-clay content soil. Tillage and crop rotation were more important than N fertilizer rate in affecting stratification ratio. These results have important implications for determining (1) soil quality in a diversity of soils around the world and (2) the impacts of crop and tillage management on soil quality.
6. Land application of municipal biosolids can sequester carbon and improve soil quality. Municipal biosolids from waste-water treatment plants are often applied to land as a means of disposal, but these materials are relatively high in carbon and nutrients, and with repeated application to the same land area could negatively affect biological quality of soils. A group of scientists from the Metropolitan Water Reclamation District of Greater Chicago and USDA Agricultural Research Service in Raleigh, NC evaluated the impact of duration (up to 33 years) and rate of municipal biosolids application on soil carbon sequestration and biological soil quality in a field study in Fulton County, Illinois. As expected, soil organic carbon sequestration was highly related to the quantity of biosolids applied. More interestingly though, biological soil quality (i.e. soil microbial biomass and its activity) was also greatly increased with increasing application rate of biosolids. These results demonstrate the strong link that occurs between soil organic carbon sequestration and the improvement in biological soil quality, as well as the enormous potential of improving soil quality with the long-term application of human-derived waste, which effectively recycles carbon and nutrients in a more ecologically compatible manner than simply land disposal or dumping. The results of this study can be used by municipalities and neighboring agricultural landowners as evidence that biosolids application on degraded farmland can recreate an ecologically robust soil system, capable of supporting a thriving soil microbial population.
7. Plant sensitivity to ozone varies throughout the day. Ozone is a toxic air pollutant that injures plants leading to reductions in growth and yield of crops, forests, and natural vegetation. Predicting ozone impacts requires knowledge of a number of interacting factors including ozone concentration in the air, leaf gas exchange that controls ozone uptake into plants, and the inherent defense capacity of the plant. Defense capacity is recognized as being a combination of metabolic and genetic components. In this study, cotton sensitivity to ozone was shown to vary throughout the day with greatest sensitivity observed in the afternoon when ambient ozone concentrations are often the highest. Evidence that plant sensitivity to ozone varies on a relatively short time scale suggests that modeling ozone impacts on vegetation should not assume plant sensitivity to be constant. Although there has been much speculation that plant sensitivity to ozone may vary over time, this study is the first to demonstrate such short term changes exist and provides the basis for future research on the underlying mechanisms that determine plant response to air pollution.
8. Interactions between plants, mycorrhizal fungi, and plant viruses are impacted by elevated carbon dioxide. It is well known that elevated carbon dioxide stimulates plant productivity and this effect is mediated by processes beyond the obvious benefit of providing more carbon for plant growth. Such processes include the simultaneous interactions between plants as host species and naturally occurring beneficial microbes as well as pathogens. Under elevated carbon dioxide, mycorrhizal association with the roots of two grass species increased the titer of viral infections, and virus infection reciprocally increased colonization of roots by mycorrhizal fungi. Additionally, virus infection decreased plant allocation to root biomass, increased leaf phosphorus, and modulated effects of carbon dioxide and phosphorus addition on mycoorhizal root colonization. The results suggest that projected increases in atmospheric carbon dioxide will likely alter the complex interactions between plants and the microbes that associate with them.
9. Productive cool- and warm-season perennial pastures can be developed with good grazing management. Development of perennial pastures composed of both cool- and warm-season grasses in the southern region would help achieve high productivity of year-round grazing systems and help avoid the high costs of cutting and making hay. Scientists with the USDA Agricultural Research Service in Watkinsville, GA and Raleigh, NC conducted a multi-year investigation of interseeding Georgia-5 tall fescue with wild endophyte infection into Coastal bermudagrass pastures in the Piedmont of Georgia. Pastures were managed with three different fertilization regimes (inorganic only, organic + inorganic, and organic only) and four different utilization strategies (unharvested, low and high grazing pressure, and hayed) for 7 years after introduction of tall fescue. Introduction of tall fescue into Coastal bermudagrass sod was successful in developing a mixed tall fescue-bermudagrass pasture system capable of greatly expanded grazing opportunities throughout the year. Days of grazing were increased from 140 days on bermudagrass pasture only to ~260 days on tall fescue-bermudagrass pasture. It appears that careful management of the wild-endophyte-infected tall fescue component is most critical in determining the balance of tall fescue and bermudagrass components, because of its tolerance to high grazing pressure from one perspective and its dominance over bermudagrass through smothering from another perspective. We conclude that mixed tall fescue-bermudagrass pastures grazed by cattle produced nearly equivalent total forage production as from separate pastures, but from half the land area. This production perspective needs to be balanced against the results of environmental analyses, which will be reported elsewhere.
10. Greater forage-based animal productivity achieved per land area with mixed forages. Small-scale cattle producers want to know how to develop year-round grazing systems with robust forage combinations that can lead to greater sustainability. Mixing bermudagrass and tall fescue are logical choices in the southern region, but information is lacking on how these forages should be managed to obtain the best results. Scientists at the USDA Agricultural Research Service in Watkinsville, GA and Raleigh, NC conducted a grazing study in which tall fescue was introduced into a 5-year-old solid stand of bermudagrass and steer performance and production were measured throughout the 12 years of investigation. Stocker grazing of mixed tall fescue-bermudagrass pastures in the Piedmont of Georgia was highly successful in achieving adequate steer performance (1.3 lb/day) and steer production (771 lb/acre). Reducing grazing pressure to increase residual forage mass resulted in a reduction in steer stocking rate from 1.7 steers/acre to 1.5 steers/acre. However, the reduction in grazing pressure was able to increase steer performance from 1.3 lb/day to 1.4 lb/day. The shift from lower steer production with low grazing pressure early in the study towards greater steer production with low than with high grazing pressure later in the study was a significant outcome of this study. We conclude that excellent cattle performance and productivity can be achieved with broiler litter fertilization of strategically grazed pastures with mixed tall fescue-bermudagrass forage composition. These results can be used by the thousands of small-scale cattle producers to improve the sustainability of grazing systems in warm, humid climates.Matthews, J., Smith, R., Fiscus, E.L. 2013. Confidence interval estimation for an empirical model quantifying the effect of soil moisture and plant development on soybean (Glycine max (L.) Merr.) leaf conductance. International Journal of Pure and Applied Mathematics. 83(3):439-464.