Document: EDW-3-59-78

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

SCHUUR, E.AG* ¹, E.SCHWARTZ ², K.MSCOW ² and P.MMATSON ³

University of California, Berkeley, CA, USA ¹
University of California, Davis, CA, USA ²
Stanford University, Stanford, CA, USA ³

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 phospholipid fatty acid analysis (PLFA), intergenic transcribed spacer analysis (ITS), and denaturant gradient gel electrophoresis (DGGE) to 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 ITS 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. Principal component analysis of PLFA also showed that the microbial communities in sites 1 through 4 were more closely related than the 2 wettest sites (5 and 6), and supported the ITS results. 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.

Keywords: soil carbon, oxygen availability, tropical forest, microbial communities, redox potential, precipitation gradient

This abstract is being presented at: 3:30 PM in session:
MICROBIAL ECOLOGY