Document: DAV-3-57-6

Changes in alpine soil microbial function and species composition during spring snowmelt

LIPSON, D.A.*, R.K.MONSON and S.K.SCHMIDT

Department of Environmental, Population and Organismic Biology, University of Colorado, Boulder, CO ¹

Abstract:
High levels of soil microbial biomass are found under snowpacks in the dry meadow communities of the Colorado alpine. During late spring when the snow pack melts, soil microbial biomass declines. Previous work showed that the decline of microbial biomass in the spring is caused by changes in temperature and carbon availability. We tested the hypothesis that the summer and winter microbial communities differ in function and species composition. Shifts in species composition between pre- and post- snowmelt communities were detected using reciprocal hybridization of community DNA. Replicate soil samples were collected from a dry meadow before and after snowmelt. DNA extracted from soils sampled at different times was significantly less homologous relative to spatial replicates sampled at the same time. To address functional changes we measured the size of various microbial functional groups throughout the year using substrate-induced growth response (SIGR) and most probable number (MPN) techniques. The microbial biomass showed different preferences for substrate use between winter and summer. The phenolic compounds, salicylate and vanillate, were used by a disproportionately higher group during the winter months. Also, the soil microbial biomass responded differently to temperature in winter and summer. The winter biomass contained a component that grew at 3 degrees C but not at 22 degrees C. Use of bacterial and fungal inhibitors showed that the biomass that responded to substrate input in the winter was predominantly fungi, while in the summer bacteria and fungi both responded. From these results we conclude that the summer and winter soil microbial communities contain different assemblages of organisms that react differently to substrate and temperature.

Keywords: microbial community structure, microbial population dynamics

This abstract is being presented at: 8:45 AM in session:
Oral Session #71: Soil Microbial Biomass and Soil Respiration.