季节性冻结初期川西亚高山/高山森林土壤细菌多样性

高山/亚高山显著的季节性冻结过程可能对土壤细菌多样性产生重要影响。为了解季节性冻结初期土壤完全冻结前后川西亚高山/高山森林群落土壤细菌多样性变化特征,于2008年11月5日(土壤冻结前期)—11月25日(土壤完全冻结期)期间,采用PCR-DGGE技术同步研究了原始冷杉(Abies faxoniana)林(PF)、针阔混交林(MF)和次生冷杉林(SF)的土壤细菌群落多样性变化特征。土壤完全冻结后,3个森林群落仍然具有较高的土壤细菌多样性。3个森林的土壤细菌类群总数在土壤冻结前表现为MFSFPF,但在土壤完全冻结后表现为PFMFSF。土壤冻结明显降低了土壤细菌多样性,但提高了土壤细菌群落的优势度。冻结作用对土壤细菌群落的影响随着土壤深度增加而降低,随着海拔升高而降低。这些结果表明季节性冻结过程对亚高山/高山森林土壤细菌多样性有着显著的影响,这对深入认识冬季土壤生态过程具有重要意义。

Soil bacterial diversity in the subalpine/alpine forests of western Sichuan at the early stage of freeze-thaw season

Significant seasonal soil freezing and thawing could influence greatly on soil bacterial diversity in the alpine/subalpine forest. To understand the characteristics and dynamics of soil bacterial diversity in the alpine and subalpine forests of western Sichuan during one onset of soil freezing, a field experiment was conducted to investigate the soil bacterial diversity by PCR-DGGE in the primary fir (Abies faxoniana) forest, fir and birch (Betula albosinensis) mixed forest and secondary fir (A. faxoniana) forest, which were three representative forests in the subalpine and alpine forest region in western Sichuan. Soil samples were collected on Nov.5 and on Nov.25, 2008, which was defined as the onset of freezing based on the simultaneous monitoring of soil temperature. Relative rich soil bacterial groups were still observed in the three sampled forests after soil freezing. The ranked order of soil bacterial groups was MF> SF> PF before soil freezing, while the ranked order was PF> MF> SF after soil freezing. Soil freezing decreased soil bacterial group and diversity, but increased soil bacterial dominance. However, the impact degree of soil freezing declined with the increase of soil depth and elevation. The results suggested that seasonal freezing had obvious effects on soil bacterial diversity in these subalpine/ alpine forests. Meanwhile, the results also implied that the dynamics of soil bacterial community during the onset of freezing was of ecological significance to understand the wintertime ecological process in soils.