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United States Department of Agriculture

Agricultural Research Service

Research Project: Soil Microbial Communities: Key Indicators of Soil C

Location: Wind Erosion and Water Conservation Research

2013 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.


3.Progress Report:

Our goal is to determine the shifts in soil microbial community composition (structure and diversity), biogeochemical processes, and soil carbon dynamics accomplished with the Conservation Reserve Program (CRP) by evaluating 26 fields representing 0 (cotton-based cropland) to 26 years of CRP. Our first soil sampling within this CRP chronosequence occurred in summer 2012, regardless of extreme climatic conditions (i.e., extended drought). Thus, our sampling also intended to determine how these systems cope with extreme climatic conditions of droughts and heat waves within the comparison among the fields-chronosequence. Preliminary findings are showing minor differences in the microbial communities and activities within this chronosequence. Although soil organic C content is not significantly affected within the CRP chronosequence, a more labile C fraction, such is the particulate organic matter (POM-C) increased from 0.6 Mg ha-1 to 1.4 Mg ha-1 for the 0- to 8-year CRP fields, but did not change from 8- to 26-year CRP fields. We hypothesize the little distinctions among the CRP chronosequence could be due to the consecutive severe drought/heat wave experienced from 2011-2012, as this region received only 150 mm precipitation in 2011 and 285 mm in 2012 compared to 400 mm yearly average. A second sampling was not conducted in these CRP fields in July 2013 because the summer started very dry again, and it would not expand our results from the 1st sampling in July 2012, which was under a drought as well. We expect to conduct a second sampling anytime in the future within the 5-year period of this study; as soon as conditions show an improvement of climatic conditions for at least a year. We performed additional analyses to the 1st sampling (i.e., pyrosequencing) for a more detail description of soil microbial community composition (diversity) to the species level. Previously, the fungal component was not going to be analyzed with pyrosequencing due to the cost and because the technique was not available for this microbial group. Currently, pyrosequencing data for fungal and bacterial data are being analyzed. In addition, we are establishing assessments of the short-term dynamics of the soil microbial community structure, biogeochemical processes, and soil carbon dynamics as CRP is converted to a row crop during the first four years. ARS is assisting graduate students from Texas Tech to investigate the changes in soil enzyme activities in this CRP chronosequence due to their role in ecosystem services related to the soil metabolic capacity: biogeochemical cycling and soil organic matter dynamics. ARS is also assisting to perform the evaluation of the changes in microbial community composition according to fatty acid methyl ester (FAME) profiles. It is very valuable to combine our resources and teams to accomplish so many different levels of comparisons of the changes in soil quality and functioning as affected by this federal program, CRP.


Last Modified: 9/2/2014
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