Monday, November 5, 2007
96-22
The Fate of Microbial Groups in Tropical and Temperate Forest Soils.
Heather Throckmorton1, Jeffrey Bird2, Mary Firestone3, and William Horwath1. (1) UC Davis, 1959 Lake Boulevard, Apt. 165, Davis, CA 95616, (2) CUNY-City Univ.of NY, Queens College, CUNY, 65-30 Kissena Blvd.,, Flushing, NY 11367, (3) University of California-Berkeley, Univ. of California, Dep. Of Espm 137 Mulford Hall, Berkeley, CA 94720
Microorganisms catalyze soil organic matter (SOM) processes through decomposition and re-synthesis of biochemical compounds, and may represent a significant proportion of source material for stable SOM. This research investigates the importance of microbial biochemistry to carbon humification pathways in two climatically different forested ecosystems, Blodgett forest (BF), a temperate forest in the Sierra Nevada and Luquillo forest (LF), a tropical forest in Puerto Rico. These sites represent diverse ecosystems that are known to support substantially different microbial communities. 13Carbon (C) enriched tropical and temperate species from four microbial groups (fungi, actinomycetes, bacteria gram(+), and bacteria gram(-)) were separately added to soil at both sites. Decomposition rates were substantially greater in LF than BF. When comparing tropical and temperate microbial additions, there were no significant differences in total-C remaining at either site, but there were differences in C-recovery within the microbial biomass-C (MBC) and the dissolved organic carbon (DOC) pools. Initial DOC and MBC recovered at BF were higher for tropical microbial treatments while LF was higher for most temperate microbial treatments. After several months, these trends reversed. Results indicate that the temperate microbial community initially consumed tropical microbial bodies more readily than temperate microbial bodies, while the tropical microbial community initially consumed temperate fungi and bacteria gram(-) more readily than tropical. Both soils respired more tropical fungi C than temperate, and more temperate actinomycetes C than tropical. There were no significant differences between temperate and tropical bacteria gram(+) C and bacteria gram(-) C recovered as CO2-C for either site. These results show potentially different stabilization mechanisms associated with microbial groups and are most likely associated with differences in microbial biochemistry. The soil microbial community plays a key role in SOM dynamics, and this research provides important insight into these relationships and the biogeochemical processes governing soil carbon dynamics.