PARENT SESSION
Oral Session #40: Carbon sequestration and flux.
Presiding: G. Koch
Tuesday, August 6. 1:00 PM to 4:45 PM. Gila Meeting Room, TCC.
Isotopic evidence for plant community alteration of C-cycling microbial functional groups in soil.
Waldrop, Mark*,1, Firestone, Mary2, 1 School of Natural Resources and Environment, Ann Arbor, MI2 Division of Ecosystem Science- ESPM, Berkeley, CA
ABSTRACT- In order to determine whether plant communities alter C-cycling microbial functional groups and processes rates, we examined the degradation of C substrates (13C-labeled starch, hemicellulose, vanillin, and pine litter) and the enhanced degradation of SOM (the priming effect) in oak canopy and open grassland soils that fostered different microbial communities. We linked microbial biomarkers to C degradation by measuring the isotope ratios of microbial phospholipid fatty acids (PLFAs). Oak canopy soils had higher rates of pine litter degradation, equal rates of starch, hemicellulose, and vanillin degradation, and lower rates of enhanced SOM degradation compared to open grassland soils. The stimulation of soil enzyme activity following substrate addition was highly related to the degradation of added substrate, but not enhanced SOM degradation. 13C-PLFA revealed that different microbial communities utilized the C substrates in the two soils. The fungal community in oak canopy soil had lower metabolic activity and did not utilize extra SOM following substrate addition, potentially explaining the microbial mechanism for a smaller priming effect in oak canopy soils compared to open grassland soils. This experiment showed that differences in microbial community composition and activity associated with different plant communities can alter the degradation rates of different pools of soil C, thus demonstrating the critical importance of microbial community ecology in C cycling research.
KEY WORDS: 13C-PLFA, enzymes, plant-microbial interations, C-cycling