林窗对凋落物分解过程中细菌群落结构和多样性的影响

Influence of Forest Gap on Bacterial Community Structure and Diversity during Litter Decomposition

基于细菌16S rDNA 的PCR-DGGE 方法,以林下（US）为对照,研究了长江上游低山丘陵区人为采伐形成的马尾松（Pinus massoniana）人工林7 种不同大小林窗（G1：100 m^2、G2：225 m^2、G3：400 m^2、G4：625 m^2、G5：900 m^2、G6：1 225 m^2、G7：1 600 m^2）在冬夏两季对凋落物分解过程中细菌群落结构和多样性的影响.结果表明,凋落物中的细菌群落结构和多样性受到林窗大小的显著影响,这种差异性受到季节的影响.有些菌纲只出现在特定大小的林窗,例如,绿弯菌纲（Chloroflexi）和放线菌纲（Actinobacteria）都只出现在US 和G1 林窗,芽孢杆菌纲（Bacilli）只出现在大中型（G4-G7）林窗,黄杆菌纲（Flavobacteria）只出现在中型（G4 和G5）林窗,浮霉菌纲（Planctomycetacia）只存在于G5、G7 和US.冬夏两季细菌群落结构差异较大,冬季的细菌类群高于夏季.在冬季,细菌群落的多样性与林窗大小、凋落物含水率、日平均温度、凋落物的全碳、可溶性有机碳和全氮含量显著相关;在夏季,细菌群落的多样性仅与日平均温度和全碳含量显著相关.总体来看,变形菌门是凋落物分解过程中的优势类群,有利于凋落物分解过程中的碳氮循环.林窗的形成改变了凋落物中的细菌群落结构和组成,减小了凋落物分解过程中细菌群落的丰富度指数、多样性指数和均匀度指数,但增大了优势度指数.冬季的细菌群落的丰富度、多样性和均匀度高于夏季,优势度则低于夏季.

The research on the bacterial community structure and diversity in litter in winter and summer was based on polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) for 16S rDNA in seven gap sizes of aPinus massoniana plantation (G1: 100 m2, G2: 225 m2, G3: 400 m2, G4: 625 m2, G5: 900 m2, G6: 1225 m2, G7: 1600 m2) in a hilly area of the upper Yangtze River. Results indicated that the bacterial community structure and diversity in litter were influenced by gap size, and this difference was also affected by the seasons. Some bacteria classes only appeared in forest gap of certain size, for example, Chloroflexi and Actinobacteria only appeared in US and G1, Bacilli only appeared in large and medium-sized (G4 to G7) forest gap, Flavobacteria only appeared in medium-sized (G4 and G5) forest gap, Planctomycetacia only existed in G5, G7 and US. The difference of bacteria community structure between winter and summer was very big. The bacteria groups of winter were more than summer. In winter, the diversity of bacterial community showed very close correlation with gap size, litter water content, daily average temperature, total carbon, dissolved organic carbon and total nitrogen content of litter; in summer, it was only related to daily average temperature and total carbon content of litter. Overall, Proteobacteria was the dominant in the process of litter decomposition, was conducive to the cycle of carbon and nitrogen in the process of litter decomposition. The formation of forest gap changed bacterial community structure and composition in litter, reduced the richness index, diversity index and evenness index of bacterial community in the process of litter decomposition, but increased the dominance index. Richness, diversity and evenness of bacterial community in winter were higher than those in summer, but dominance was lower than that in summer.