Monitoring Soil Microbial Dynamics in Agroecosystems during Two Years of Recovery after Record Drought.

We monitored soil microbial dynamics in six agroecosystem in the Southern Plains of the U.S. during climatic recovery after four years of record drought.  Our previous study provided some of the first information that linked significant reductions in soil enzymatic potential and microbial diversity directly to a drought and heat wave; however, no information is available on the changes in microbial dynamics during a drought recovery period.  Over 8 sample times during two years when the Palmer Drought Severity Index changed from severe drought to exceptionally wet, we found seasonal and moisture-based fluctuations in microbial biomass C-N and fatty acid (FAME) indicators, while enzyme activities (b-glucosidase, b-glucosaminidase, Alkaline phosphatase, Arylsulfatase) remained relatively constant.  When averaged across all sites, total FAME fluctuated less than microbial biomass C-N, though fungal FAMEs showed the most variation during both years.  Overall, there was no clear trend of changes in enzyme activities or microbial community size and structure during this two year recovery period.  We hypothesize that this is due to the lack of available substrates, which were severely depleted during the drought as crop establishment was not possible and no biomass was returned to these soils for multiple years.  We are continuing to monitor these sites and will evaluate microbial diversity using Illumina sequencing.