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 (Steenwerth et al., 2003, Soil Biology and Biochemistry). 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, suggesting that labile soil organic matter affects microbial composition.

References

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.

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