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.

Microbial communities on a precipitation gradient: Links to soil redox and carbon cycling.

Schwartz, Egbert^*,1, Schuur, Edward², ¹ University of Denver, Denver, CO² University of Florida, Gainesville, FL

ABSTRACT- Soil carbon pools have been observed to increase with increasing precipitation in humid upland ecosystems where water availability is likely to exceed plant demand. On a precipitation gradient in Hawaii, our previous work linked increased carbon pools to decreased rates of decomposition as a result of limited soil oxygen availability. Across this natural gradient of rainfall, we used the Terminal Restriction Fragment Length Polymorphism (TRFLP) to characterize the bacterial, fungal and archaeal communities and ask the question 1) how does microbial community composition change with increasing moisture availability, and 2) how do changes in microbial community relate to changing decomposition rates and the availability of soil electron acceptors? We characterized soil microbial communities from six sites in Hawaiian montane rainforests similar in temperature regime, plant species composition, substrate age, and parent material while mean annual precipitation ranged from 2200 to 5100 mm/yr. Cluster analysis of the TRFLP patterns demonstrated that the relatedness of microbial communities changed gradually with increased precipitation, and that the microbial community at any site was most closely related to sites with similar rainfall regimes. These patterns corresponded with median soil reduction oxidation potentials across the gradient that ranged from +420 mV at site 1 to −150 mV at site 6, indicating that soils were predominantly aerobic at the mesic end of the gradient and anaerobic at the wet end of the gradient. These data suggest that microbial communities may reflect the availability of electron acceptors in soils, and may be useful as an integrative measure of limited oxygen availability in upland soils.

KEY WORDS: Microbial communities, Carbon cycle, Soil redox, TRFLP