Document: MAR-3-6-6

Plant C meets microbial N-tranformations in rhizosphere soil.

FIRESTONE, M.*

University of California, Berkeley ¹

Abstract:
Microbial populations and activities are elevated in soil near plant roots due primarily to enhanced availability of labile carbon from root exudates and debris. The effects of plant-originated carbon on N-immobilization, mineralization, and nitrification are of dominant importance in this soil compartment, yet are temporally and spatially highly dynamic. Prevailing theories state that under high carbon availability, gross immobilization of N into microbial biomass would predominate; under conditions of low carbon availability, microbial starvation processes will result in release of NH4+. However, a variety of alternative mechanisms complicates an already spatially and temporally complex picture. Microfaunal grazing of bacteria/fungi and drying/wetting cycles can also result in release of NH4+ due to utilization of nitrogen-containing organic compounds for energy generation. If rhizosphere microbes access organic N from soil sources, then this would also contribute to the localized N-cycle in rhizosphere soil. Recent work on root carbon flow, bacterial populations, and protozoal biomass, begins to relate the spatial and temporal dynamics of these rhizosphere players to rates of N-transformations in this important soil compartment.

Keywords: nitrogen,microorganisms,rhizosphere

This abstract is being presented at: 8:45 AM in session:
Symposium # 21: The Rhizosphere: Top-Down and Bottom-Up Approaches.