Document: DOU-3-65-34

Microbial activity and nitrogen dynamics in a California annual grassland, coastal sage scrub and mixed oak woodland community.

DORNELLES, D.S.* and J.P.SCHIMEL

University of California, Santa Barbara, CA 93106, USA ¹

Abstract:
California's coastal valleys have a complex mosaic of plant communities, with potentially complex relationships between soil characteristics and the plants present. Many of these communities, particularly at the grass-sage scrub interface, have abrupt and discrete boundaries. Our research was designed to understand and describe the role by which soil characteristics affect and are influenced by the distributions of these plant communities. Forty five soil samples collected beneath three different plant communities along six transects at Sedgwick Ranch Natural Reserve near Santa Barbara, California, in late March of 1999, and lab assays were conducted to measure soil physical characteristics, carbon and nitrogen mineralization rates, nitrification potentials, soil ammonium/nitrate and organic carbon and nitrogen content. Grass soils were 10% higher in clay than those of either oaks or sage, though water holding capacities did not differ. Oak soils were significantly more acidic than the other soils. Carbon mineralization rates were higher under oaks than grass or sage scrub soils. Net N-mineralized was highest for grassland soils, followed by oak soils and sage soils. Chloroform labile biomass-N was highest for grass soils and lowest for sage soils. Chloroform labile biomass-C was highest for oak soils, with sage lowest at the beginning of the lab incubations.

Keywords: Sage scrub, N-mineralization, N dynamics,Annual grassland

This abstract is being presented at: 3:30 PM in session:
MICROBIAL ECOLOGY