Changes in soil microbial biomass and bacterial diversity during the transition from winter to growing season in the subalpine/alpine forests

Changes in microbial community from winter to growing season are helpful to understand their self-adaptations in the high-frigid ecosystem. A field experiment was conducted to investigate soil microbial biomass and bacterial diversity by PCR-DGGE in the primary fir(Abies faxoniana) forest (PF), fir and birch (Betula albosinensis) mixed forest (MF) and secondary fir forest (SF) in western China. Soil samples were collected in March, April, May and August, 2009. The microbial biomass C (MBC) in soil organic layer (OL) increased from winter to growing season, but insignificant changes were observed in soil thawing period (April and May). In contrast, MBC in soil mineral layer (ML) displayed an obvious decrease at the end of soil thawing (May) and then increased. Rich DGGE bands indicating rich bacteria populations have been detected even under completely soil frozen condition. The richness of bacteria community significantly decreased during soil thawing period and then increased to growing season, except for which in OL of MF. The similarity of bacterial communities implied significant community changes during the transition, showing more sensitivity to temperature than forest type and soil layer. The results here are of ecological significance in explaining the adaptation of microorganisms in the high-frigid areas.   Key words: Microbial biomass, bacterial diversity, soil thawing period, alpine forest, freeze-thaw events.