Soil microorganisms carry out many processes that are vital for maintaining productive soils and sustainable agricultural lands. For example, they recycle nutrients and regulate greenhouse gas emissions. However, little is known about the distribution of microorganisms across the landscape. To address this knowledge gap, this research project will study how different factors, such as agricultural management practices and soil properties, influence the distribution and function of microorganisms at local and broader spatial scales. The experiments will be conducted as part of the Landscape Biomass Project, a large-scale research and demonstration farm in central Iowa. Results from this project will generate data for modeling soil microbes and the processes that they perform. These models, in turn, will inform management decisions that promote soil carbon and nitrogen retention and minimize greenhouse gas emissions.
Data collected as part of this project will strengthen cross-disciplinary research that involves the fields of ecology and biogeochemistry, agronomy, hydrology, forestry, and economics. The project will support international collaborations with soil modelers in the United Kingdom. It will foster training of undergraduate students in the biogeochemical sciences through hands-on field and laboratory experience. Finally, results will be presented to a diverse group of public and private stakeholders at on-site field presentations, meetings with a farmer advisory board, and at workshops with policy makers.
Microbial communities are at the heart of important ecosystem functions. Soil microbes are intimately involved in the recycling of nutrients: they decompose organic matter into plant available nutrients, retain these nutrients in the soil, and regulate the production of greenhouse gases. In order to understand how microorganisms influence these ecosystem functions, we first need to characterize how they interact with the soil environment. Therefore, understanding the factors that shape the spatial distribution of microbial communities is needed, and is especially important for the long-term economic and ecological health of agricultural ecosystems. The goal of this research was to characterize the response of soil microbial communities to factors (plants, soil properties) that influence their spatial distribution in agricultural ecosystems. To address this goal, we conducted studies at the Landscape Biomass Project, Boone County, IA, using an annual (continuous corn) and perennial (switchgrass) cropping system replicated at three locations along a hill. In addition, we used spatial modeling to understand the effect of cropping systems on variation in microbial communities along a transect. By sequencing microbial DNA extracted directly from soil, we generated data sets that characterize microbial communities, and identified over 6,000 bacteria taxa per soil sample. Based on these data, we found that the overall composition of soil microbial communities was driven mostly by soil factors associated with location on the hill. When fully grown, plants influenced a small subset of the microbial community involved in nutrient recycling. The consequences of the observed plant-effects are not yet known, but our data suggest that small changes in the microbial community may have important consequences for nutrient recycling and, therefore, plant growth and health. Further, our data identified candidate microbial taxa for future studies targeting these plant-microbe relationships. Spatial modeling indicated that environmental variation at fine scales structures microbial communities and the activity of enzymes associated with nutrient recycling. From this scale-specific modeling, our data suggest the importance of microbial abundance to enzymes involved in the recycling of nitrogen and phosphorus and microbial community structure to enzymes involved in the recycling of carbon. Results highlight the importance of scale to understanding the microbial ecology involved in ecosystem functions, which has implications for managing for important microbial functions on agricultural land. This research trained two female undergraduate students in molecular and biogeochemical soil analyses and scientific interpretation, and we presented results of this project at public seminars in central Iowa.
