2007 Annual Report 1a.Objectives (from AD-416) 1) Characterize the functional and population ecology of microorganisms involved in the degradation of herbicides, ecology of weed seed banks, and biogeochemical cycling of soil nitrogen, as these activities relate to the development of integrated weed management systems that employ more biologically based approaches. . 2)Measure the effects of soil factors (which may be constant, dynamically fluctuating, or periodically recurring) that respond to agricultural management, natural climate and physicochemical conditions (including water/oxygen regime and fertility management) on the fate of herbicides. 1b.Approach (from AD-416) Proposed experiments will. 1)investigate key populations of herbicide degraders under a variety of soil conditions,. 2)determine the ecological (functional) significance of these populations in natural soil as they respond to changes in the environment, and. 3)allow long-term temporal monitoring that will link microbial populations and their physiological response to management and seasonal/climate effects. The plan includes eight tasks, each of which addresses, in part, one or both project objectives. Two tasks (V and VIII) serve other ARS projects, one at another ARS location and the other part of a cross-location project. All tasks include laboratory measurement, however, Tasks II and VII involve treatments/variability imposed in the field. Treatments for remaining tasks will be introduced in the laboratory. 4.Accomplishments 1. Ecology of Atrazine Degradation in Soil. Many of the processes affecting the behavior of herbicides in the environment are mediated by microorganisms, however little is known as to how environmental conditions or management practices regulate herbicide fate at the organism level. Factors controlling atrazine degradation were examined in soil from an atrazine spill, using soil process and microbial ecology measurements. The soil exhibited a high rate of atrazine degradation accompanied by accumulation of degradation products (hydroxyatrazine and cyanuric acid), and biodegradation was limited primarily by bioavailability. A bacterial isolate, ES-1, obtained from the soil, quantitatively converted atrazine to cyanuric acid (via hydroxyatrazine), as predicted by atrazine degradative genes that were detected in the organism. A gene sequence (16S rRNA gene) confirmed that ES-1 is closely related (99%) to Arthrobacter species. Terminal restriction fragment length polymorphism (T-RFLP) analysis of soil DNA revealed fragments consistent with Arthrobacter species, though no enrichment of these fragments was observed when stable isotope probing was performed using 15N-ethylamino-atrazine. These experiments will be valuable in determining factors affecting herbicide degradation in soil, as they provide a framework for assessing how microbial populations involved in herbicide degradation may be affected or change in activities as environmental or other factors change. This accomplishment addresses NP 202, Component 4, Soil Biology, Problem Statements 1 (Improved Understanding of Soil Biology and Rhizosphere Ecology) and 7 (Managing Pesticides in Soils). 2. Anaerobic degradation of herbicides in soil. Many soils in the upper central cornbelt region of the U.S. are characterized by slow permeability and poor drainage. Rainfall events can often result in localized flooding leading to temporal zones of anoxia in the soil. The fate of herbicides under anaerobic conditions has not been well-studied. To determine the potential for anaerobic degradation of several herbicides, we examined bacterial populations such as Anaeromyxobacter dehalogenans and Desulfitobacterium spp., known for their anaerobic reductive dehalogenation activities, and assessed their functional role in soils with long commercial cropping histories. Herbicides included bromoxynil, dicamba, atrazine, and 2,4-D, along with the precursor used in synthesis of many herbicides, 2,6-dichlorophenol. Experiments to measure the reductive dehalogenation of the selected herbicides by seven distinct strains of A. dehalogenans have been completed, and results of soil enrichment studies demonstrated that members of this bacterial group are commonly found in all soils tested. Further, the presence of A. dehalogenans and their demonstrated ability to reductively dehalogenate herbicides correlated with the functional activity measured in soils. This accomplishment addresses NP 202, Component 4, Soil Biology, Problem Statements 1 (Improved Understanding of Soil Biology and Rhizosphere Ecology) and 7 (Managing Pesticides in Soils). 3. N management effects on weed growth and seedbank dynamics. Field and laboratory studies were conducted to quantify the impact of manipulating soil inorganic N levels on weed growth and weed seedbank dynamics. The influence of N fertilization on weed growth and interference with crop yield varied with background soil N fertility levels, while N fertilizer effects on weed seed decay were found to vary widely by weed species. These findings are important as they help to define recommendation domains for attempting to manage weed problems via N fertilization strategies. This accomplishment addresses NP 202, Component 4, Soil Biology, Problem Statements (Improved Understanding of Soil Biology and Rhizosphere Ecology). 5.Significant Activities that Support Special Target Populations None. 6.Technology Transfer Number of web sites managed 1 Number of non-peer reviewed presentations and proceedings 3 Number of newspaper articles and other presentations for non-science audiences 1 Review Publications Davis, A.S., Kenner, K. 2007. Seed depth and pathogens affect fatal germination of velvetleaf and giant foxtail. Weed Science. 55:30-35. Cupples, A.M., Sims, G.K. 2007. Identification of In Situ 2,4-Dichlorophenoxyacetic Acid-Degrading Soil Microorganisms Using DNA-Stable Isotope Probing. Soil Biology and Biochemistry. 39:232-238.