1a. Objectives (from AD-416)
Objective 1: Measure effects of management, climate, and soil conditions on microbial processes (herbicide degradation, nitrogen cycling, and weed seedbank dynamics) in corn/soybean ecosystems. Objective 2: Evaluate the effects of management and climate change on the biology and ecology of weedy and invasive species, including potential weedy cellulosic bioenergy crops, in Midwestern cropping systems. Objective 3: Identify effective combinations of weed management components through application of both new and existing knowledge that exploit useful plant and environmental interactions in vegetable cropping systems.
1b. Approach (from AD-416)
Each objective of the proposed work seeks to advance knowledge of specific topics that directly or indirectly relate to weed-crop competition for resources, providing a basis to identify tactics of routine management that shift the competitive advantage to the crop. We examine the ecology of microorganisms and plants, and combine these efforts into a synthesis that applies research findings toward practical solutions. Each objective utilizes the whole scientific team, and regardless of scale, experiments include samples from a common group of sites, providing extensive metadata support. Studies under Objective 1 address microbial activities that are influenced by agricultural management, climate, or soil conditions. Primary climatic factors to be addressed are temperature and rainfall. In Objective 2, management and climate change will be evaluated as to effects on the biology and ecology of weedy and invasive species, including potential weedy cellulosic bio-energy crops, in Midwestern cropping systems. A particular focus will be on spatiotemporal variation in demographic parameters and population growth rates at multiple levels of scale. As a means of unifying observations, whole life cycles of weeds will be the unit of study whenever possible. Objective 3 identifies effective combinations of weed management components through application of both new and existing knowledge that exploit useful plant and environmental interactions in vegetable cropping systems.
3. Progress Report
We made substantial progress initiating investigations of weed management in a changing climate in FY 11. Design for laboratory soil microcosms for use in assessing herbicide biodegradation and microbial N-cycling under varying flooding/drainage cycles was established for use in parallel with in-situ studies at our two designated field locations. Biomarkers for reductive dehalogenating populations (which may contribute to herbicide degradation) and genes involved in nitrous oxide reduction have been validated. Over 40 new bacterial nosZ gene sequences (encoding variations of a denitrification enzyme) and ten 16s rDNA gene sequences of phenol-degraders (used for identification) were submitted to National Center for Biotechnology Information GenBank. New velvetleaf and giant ragweed seed studies are underway. Experiments were conducted to determine the ecology of organisms that degrade organic pollutants structurally related to herbicides at different depths in the profile of a major landfill in Medellin, Columbia. This site had unique features that allowed measurements to be made in aerobic and anaerobic environments as well as to relate the microbial results to chemical analyses of the soil matrix. The novel method of DNA-based stable isotope probing was used to determine the identities of organisms degrading pollutants at different depths. The potential impacts of more frequent soil saturation (due to climate change) on stability of soil-applied herbicides were explored using radioisotope techniques. Working with research partners throughout the southern U.S., we collected numerous seed accessions of Palmer amaranth and shattercane and grew them in a common environment in Urbana, IL, for seed increase to support weed-crop interference experiments. Special care was taken to avoid introducing a seedbank for these species. We also planted Miscanthus giganteus and Miscanthus sinensis in old field and forest environments in central Illinois, again with special procedures to minimize invasion risk, for the purpose of studying the demography and spread of these bioenergy crop species in non-crop environments. Finally, we continued our work on the management and environmental risk factors associated with the evolution and spread of glyphosate resistant waterhemp in Illinois grain crops, screening dozens of accessions for glyphosate resistance, and recording management histories for the farms from which they came. The results of work done thus far puts the research on track to deliver solutions for emerging questions in weed management due to exploitation of new biofuel feedstocks, climate change, and weed adaptation to existing management strategies.
1. Stewardship guidelines for safe bioenergy crop production. Herbaceous perennial grasses grown for bioenergy purposes can provide huge amounts of biomass, but also have the potential to become invasive if not managed carefully. ARS researchers at Urbana, IL, provided technical support to the MFL A Aloterra Company and Biomass Crop Assistance Program (USDA-Farm Services Agency) that was based on ARS research on the invasive potential of bioenergy crop species. ARS researchers measured vital rates and dispersal characteristics of Miscanthus and used this information to help guide the design of bioenergy plantations and surrounding buffer areas. Production issues addressed by the plan included guidelines for safe siting of production plantations, specifications for the width of buffer zones surrounding production fields, and eradication of plantings, among others. These suggestions were taken into consideration and incorporated into the conservation plan for a new 50,000 acre pilot project in the Midwest supported by the USDA Farm Services Agency through its Biomass Conversion Assistance Program. This is the first large-scale production effort of herbaceous perennial biomass crops for bioenergy production. There has been considerable concern that these crops may become invasive, so the ARS effort to ensure safe production of these crops help protect the public and public lands from unwanted biological invasions.
2. Degradation of aromatic pollutants at different depths in the soil profile. The Moravia Hill landfill site at Medellin, Columbia was a long-term mixed waste site (industrial and municipal waste) that has been home to thousands of human inhabitants for decades. The population is being resettled and the site being remediated. Part of the criteria for remediation of the organic contaminants at the site was the presence of a diversity of organisms that could degrade the pollutants, a question which can best be addressed with the use of DNA-based stable isotope probing. Developed in the past decade, SIP has made it possible to identify organisms responsible for particular activity in soil. The ARS lab at Urbana is among a few laboratories world-wide suited to conduct this research, and the research questions to be addressed at the site are highly relevant to research objectives on the effects of water regime on microbial degradation processes. Clear differences in the dominant groups of degraders were observed as a function of depth and the presence of oxygen at the site. Stable isotope probing demonstrated multiple groups of degraders at each depth, and the differences in dominant organisms were well correlated to chemical conditions at each depth. These findings were used to determine the manner in which the site would be remediated, and are being applied to understand the impact of water regime on the ecology of herbicide degradation. The impact of organic carbon buried at a depth of 20 meters was in good agreement with the only published article on the microbiology of paleosols (buried soils), which occur throughout the Midwest, where they contribute to subsurface nitrogen contamination through organic matter decomposition. These results show how dominant pollutant-degrading microorganisms will be expected to shift with environmental conditions, and have great potential to explain microbial transformations of groundwater pollutants at paleosol sites in the Midwest.
Quinn, L.D., Matlaga, D.P., Stewart, R., Davis, A.S. 2011. Evaluating the influence of wind speed on caryopsis dispersal of Miscanthus sinensis and Miscanthus x. giganteus. Journal of Invasive Plant Science and Management. 4(1):142-150.