中文摘要：

应用稀释平板法和16S RNA序列分析法对不同密度杂种落叶松长白落叶松又日本落叶松人工林2种孔径凋落袋,即上层网孔2 mm、下层网孔1 mm的异孔分解袋和网孔均为1/300 mm的同孔分解袋中凋落物分解过程中土壤细菌群落及多样性进行研究.结果表明：土壤细菌数量因凋落物分解而发生明显变化（F=10.97,P＜0.01）,其中以芽孢杆菌、假单胞菌、葡萄球菌为代表的纤维素、半纤维素分解菌数量最多.2种孔径凋落袋下菌落的变化不一致：同孔分解袋中菌落随造林密度加大而增多,优势现象明显;异孔分解袋中菌落数随造林密度增加而减少,优势现象不显著.土壤细菌的组成与多样性主要受采样时段影响.不同密度杂种落叶松林土壤细菌群落具有很高的相似性.造林密度对2种凋落袋分解过程中土壤细菌群落的多样性与复杂性影响不一致.典型相关分析表明：土壤细菌群落生存的环境条件较为相似,土壤K对土壤细菌分布影响最大,土壤C/N对土壤细菌分布影响最小.

英文摘要：

Soil bacteria community and their diversity were studied during the leaf litter decomposition of Larix olgensis x Larix kaempferi plantation with different densities by two mesh size of litterbags, that is, top layer of 2 mm mesh and bottom layer of 1 mm mesh （mixed mesh litterbag）, as well as 1/300 mm mesh size（ same mesh litterbag）of litterbags. The bacteria were investigated with the plate cultivation method and PCR-16S RNA sequence analysis. The result showed that the number of soil bacteria was changed significantly （ F = 10.97, P 〈 0.01 ） during leaf litter decomposition. The bacteria participating in cellulose, hemicellulose decomposition, such as Bacillus, Pseudomonas, Staphylococcus, was the most dominant. The variety of bacteria community was not consistent between the two types of litterbags. The number of bacteria in the same mesh litterbag increased with the plantation density and some species were obviously dominated, while the number of bacteria in the mixed mesh litterbag decreased with the plantation density and there were no significant dominant species. The composition and diversity of soil bacteria community were mainly influenced by the sampling period. Soil bacteria communities were similar among the different densities of Larix olgensis x Larix kaempferi plantation. The plantation density had different effect on soil bacterial diversity and complexity during leaf litter decomposition of two types of litterbags. The canonical correlation analysis showed that the environmental conditions suitable to soil bacterial community were similar. Soil potassium had the most effect on distribution of soil bacteria, while the ratio of soil carbon tonitrogen had the least effect.