2012 Annual Report
1a.Objectives (from AD-416):
Our long-term goal is to expand and dovetail our current research approaches to characterize and identify keystone microbial community assemblages associated with enhanced ecosystem functionality, including C transformation and sequestration and key enzymatic activities involved in biogeochemical process.
1b.Approach (from AD-416):
About 26 Sites will be selected with representative soils from the Texas High Plains, which are currently under and recently out of CRP for different years. Deep soil sampling (1-2 m depth) will be used to assess the spatial distribution of soil C stocks (organic and inorganic) and associated microbial communities. Soil C stocks will be measured via an aggregate fractionation method, which separates free soil organic matter (SOM) from SOM occluded by macro-and micro-aggregates and clay and silt microstructures. Soil microbial biomass C, soil enzyme assays and quantitative PCR techniques targeting C cycling will aid in short-term evaluations in microbial functionality and C mineralization of residues and SOM. In addition, novel pyrosequencing analyses of the bacterial and fungal communities will be utilized to characterize microbial diversity.
This research is intended to provide information to select alternative management that reduce soil erosion and improve soil quality in the Semiarid Texas High Plains using Integrated Crop and Livestock Systems with enhanced soil carbon sequestration and microbial diversity. Three integrated crop-livestock systems are being compared to two continuous cotton systems in terms of soil C sequestration potential, greenhouse gas emissions and bacterial diversity.
The first soil sampling in 2010 was completed, but the second year sampling in 2011 was not possible due to an extreme historical drought that caused crop abandonment in this region. Our 2010 sampling, however, is suitable to provide information of the longterm management effects of these systems in the soil parameters included in our study.
To compensate for the lack of a second year of sampling, we expanded on the pyrosequencing assessments performed in soil samples taken in 2010 to characterize not only bacterial diversity but also the fungal diversity of soil. This can provide more robust evaluation of the entire microbial community under these integrated crop-livestock systems. Adding the fungal component is unique and represents an understudy component important in nutrient dynamics, C storage, and soil stabilization. Given the relative long-term nature of our study sites, more detailed assessments of the community, chemical composition, and functional capabilities provides details unexplored in similar systems published in the literature. The soil fungal community is known for its sensitivity to disturbance, pollution, and environmental changes and has been labeled as an exceptional indicator group for determining changes in ecosystem functioning.
Data from different assessments is being analyzed to compare the systems in terms of the microbial community size (microbial biomass C), structure (fatty acid methyl ester (FAME) profiling), and diversity of bacterial and fungal communities (pyrosequencing). We also established collaboration with another ARS soil scientist/location to analyze the soil chemical composition using Fourier Transformed Infrared Spectroscopy (FTIR). This collaboration allowed us to begin linking the microbial communities with the chemical composition of soil organic matter (assessment of soil quality).