毛竹林集约经营对土壤固碳细菌群落结构和多样性的影响

为揭示毛竹集约经营对土壤固碳细菌的影响,分别采集集约经营时间为0、10、15、20年和25年的毛竹林土壤(0—20 cm和20—40 cm)土壤,应用实时荧光定量PCR、T-RFLP以及cbbL基因文库方法,分析毛竹林长期集约经营过程中土壤固碳细菌丰度和群落结构多样性的变化,通过冗余分析(RDA)探讨影响土壤固碳细菌群落的主要环境因素。结果表明,长期的集约经营显著提高了毛竹林表层和亚表层土壤的养分含量,土壤pH值却明显降低。集约经营毛竹林土壤固碳微生物数量并未表现出与SOC的相关性,而与N素水平的变化显著相关。具体表现为:随着集约经营的进行表层cbbL基因丰度呈先上升(10年)后下降的规律,与氮素水平呈正相关(P0.05);亚表层土壤cbbL基因丰度则呈直线下降的趋势,与C∶N呈正相关(P0.05)。集约经营导致表层和亚表层土壤微生物群落结构改变,表层固碳细菌多样性指数下降。由系统发育分析可知,不可培养固碳细菌占56%比例,土壤中共同的优势种类多为变形菌和放线菌,以兼性自养为主。RDA分析结果表明土壤酸化和养分积累是毛竹林土壤固碳细菌群落和多样性变化的重要原因。

Effects of intensive management on the community structure and diversity of CO2-assimilating bacteria in a Phyllostachys pubescens stand

We examined the relative effects of long-term (25 years) intensive management on abundance and diversity of soil CO₂-assimilating bacteria in a Phyllostachys pubescens (moso bamboo) forest. Soil samples in moso bamboo stands receiving 0 (control; CK), 10, 15, 20, and 25 years of intensive management were collected from the topsoil (0-20 cm) and subsoil (20-40 cm) layers separately and analyzed using quantitative PCR (q-PCR), terminal restriction fragment length polymorphism (T-RFLP), and a clone library of the cbbL gene. Differences in the community structure of CO₂-assimilating bacteria over time and its relationship with soil properties were detected using redundancy analysis (RDA). We found that long-term intensive management significantly increased soil nutrient content but decreased soil pH. Among the soil parameters measured, N content influenced cbbL abundance, but soil organic carbon (SOC) did not. During the intensive management process, the bacterial cbbL abundance in topsoil increased in the first 10 years and then decreased, and it correlated positively with nitrogen levels (P < 0.05); conversely, in subsoil, cbbL abundance decreased linearly with time and showed a positive correlation with C:N ratio (P < 0.05). Intensive management of P. pubescens altered the community structure of CO₂-assimilating bacteria in both topsoil and subsoil, and induced a decline in the species diversity indices of CO₂-assimilating bacteria in topsoil. The results for the cbbL clone library indicated that uncultured bacteria accounted for up to 56% of the species present. The dominant species in the soil were facultative autotrophic bacteria such as Proteobacteria and Actinobacteria. RDA indicated that the changes in community structure and diversity of CO₂-assimilating bacteria resulted from soil acidification and nutrient accumulation.