PARENT SESSION
Oral Session #59: Soil Ecology: Microbial and Invertebrate.
Presiding: M. Rillig
Wednesday, August 7. 8:00 AM to 11:30 AM. Palo Verde Room, Radisson.
Soil is more than skin deep: Microbial community structure and C dynamics in a soil profile.
Fierer, Noah*,1, Schimel, Joshua1, Holden, Patricia1, 1 University of California, Santa Barbara, CA
ABSTRACT- Most studies in soil microbiology have focused on the surface 25 cm of soil, largely ignoring the greater depths. The soil profile may be many meters deep with significant amounts of nutrients and microbial biomass at depth, yet we know little about the composition and activity of microbial communities through the profile. The goal of this study was to characterize microbial communities throughout the soil profile and to determine if changes in community composition are linked to functional changes in carbon processing with depth. We studied a 2 m deep profile located in an annual grassland near Santa Ynez, California, USA. Extracted phospholipid fatty acids show that microbial communities at depth are fundamentally distinct from those at the surface, with overall diversity and richness decreasing with depth. The ratio of monounsaturated : saturated phospholipids also decreases with depth, suggesting that the microbial communities in the subsurface are severely resource limited. The changes in microbial community structure with depth parallel functional differences in microbial carbon processing. Microbial communities at depth have lower carbon substrate use efficiencies, are more limited in their ability to mineralize a diverse array of C substrates and show greater increases in respiration rates with increasing temperatures (higher Q10 values). Also, we find that the degree of nitrogen limitation to microbial respiration increases with soil depth, suggesting that additional N inputs to soil could have particularly important implications for carbon sequestration in the subsurface.
KEY WORDS: soil profile, PLFA, carbon cycling, nitrogen cycling