Kerri Steenwerth, Louise Jackson, Francisco Calderón, Mark Stromberg, Kate Scow

Microbial community composition, soil physical and chemical characteristics, management factors, and vegetation type with were investigated on irrigated and non-irrigated agricultural sites, non-native annual grasslands and relict, never-tilled or old field perennial grasslands. All 42 sites were on loams or sandy loams of similar soil taxa derived from granitic and alluvial material.

Microbial community composition was assessed with phospholipid ester-linked fatty acid (PLFA) analysis, which uses the cell membrane lipids within microorganisms as biomarkers for specific groups of organisms, thereby creating a profile or fingerprint of the microbial community. Certain fatty acids can serve as markers for specific microbial groups and as indicators of microbial stress. The total concentration of PLFA can be used as a measure of viable microbial biomass, since phospholipids are readily degraded after cells die. The results showed:

• Higher values of total soil C, N, and microbial biomass (total PLFA) and lower values of soil pH occurred in the grassland than cultivated soils.
• Distinct microbial communities exist on the various land use types based on PLFA profiles, soil characteristics, and site and management factors.
• Differences in soil microbial community composition were highly associated with total PLFA, indicating that labile soil organic matter affects microbial composition.

References
 
Drenovsky, R.E., K.L. Steenwerth, L.E. Jackson, and K.M. Scow. Land use and
     climate factors structure regional patterns in soil microbial communities. In
     press, Global Ecology and Biogeography.

Steenwerth, K.L., L.E. Jackson, E.A. Carlisle, and K.M. Scow. 2006. Microbial
     communities of a native perennial bunchgrass do not respond consistently
     across a gradient of land-use intensification.  Soil Biology and Biochemistry 38:   
     1797-1811. ucce.ucdavis.edu/files/filelibrary/5472/28052.pdf

Steenwerth, K.L., L.E. Jackson, F.J. Calderón, K.M. Scow, and D.R. Rolston. 2005.
     Response of microbial community composition and activity in agricultural and
     grassland soils after a simulated rainfall. Soil Biology and Biochemistry 37:
     2249-2262. ucce.ucdavis.edu/files/filelibrary/5472/28053.pdf

Steenwerth, K.L., L.E. Jackson, F.J. Calderón, M.R. Stromberg, and K.M. Scow.
     2003. Soil microbial community composition and land use history in cultivated
     and grassland ecosystems of Coastal California. Soil Biology and Biochemistry
     35:489-500. ucce.ucdavis.edu/files/filelibrary/5472/21425.pdf