PARENT SESSION
Poster Session #26: Soil Ecology I.
Tuesday, August 6. Presentation from 5:00 PM to 6:30 PM. Exhibit Hall B & C, TCC

Effects of vegetation and seasonality on microbial community structure and nitrogen dynamics.

Steenwerth, Kerri^*,1, Jackson, Louise¹, Scow, Kate¹, ¹ University of California-Davis, Davis, Ca.

ABSTRACT- How do plants and seasonality affect soil microbial community composition, biomass and activity, and the associated nitrogen (N) dynamics? Plant presence and functional type may affect N dynamics and potential for N loss due to contrasting plant phenology and morphology. Seasonality is expected to influence plant-microbe relationships through changes in temperature and rainfall. In the Mediterranean climate of California, we studied five land use types representing a gradient of land use intensity and soil disturbance to address the relationship between plants, seasonality and microbial community structure and biomass, and N dynamics. In increasing intensity of soil disturbance, the land use types include a relict stand of perennial bunchgrasses, a restored perennial grassland, an exotic European annual grassland, perennial bunchgrass agriculture, and conventional vegetable agriculture. The sites share the same sandy, granitic soil type but differ in total soil carbon (C) and N, pH, microbial biomass C measured as phospholipid ester-linked fatty acids (PLFA) and plant community structure. Plants were removed from small plots at each site to compare soils with and without plants. Sites were sampled in fall, winter and spring from October 2000 to March 2001 for microbial biomass C, PLFA, inorganic N, net mineralizable N, soil respiration, soil moisture, and plant biomass. Differences in soil microbial community structure, biomass, activity and N dynamics will be discussed in relation to land use history, seasonality, and plant community structure.

KEY WORDS: nitrogen , microbial community structure, agriculture, grasslands