固氮树种对第二代桉树人工林土壤微生物生物量和结构的影响

为了探究固氮树种对我国南方亚热带地区第二代桉树人工林土壤微生物生物量和结构影响及其机制,采用磷脂脂肪酸分析方法分别在干季和湿季研究了第二代桉树纯林和第二代桉树/固氮树种混交林的土壤微生物群落生物量和结构。结果表明:与纯林相比,混交林土壤(0 10 cm)的有机碳含量、铵态氮、硝态氮、总氮、凋落物生物量分别提高了17.77%、41.62%、85.59%、25.38%、19.12%,除土壤有机碳外,其它在统计学上均达到了显著性差异(p0.05);混交林的细菌生物量显著增加,但其真菌生物量显著减少;同时,混交林的总细菌、革兰氏阳性细菌相对百分含量在干季显著提高,真菌的相对百分含量却显著降低;但在湿季,除总细菌外,其它微生物群落结构没有显著差异。主成分分析(PCA)表明:第二主成分轴能明显把第二代桉树混交林和纯林的土壤微生物群落区分开来(p0.05),这种差异主要体现在混交林具有较高的细菌相对百分含量和相对较低的真菌相对百分含量。冗余度分析(RDA)表明:凋落物生物量、凋落物C/N、铵态氮、有机碳含量是驱动我国南方第二代桉树人工林土壤微生物群落结构发生变化的主要因子。此外,壕沟切根试验表明根系及其分泌物可能是第二代桉树人工林土壤微生物的重要碳源。

Effects of N-fixing Tree Species on Soil Microbial Biomass and Community Structure of the Second Rotation Eucalyptus Plantations

In order to determine the effects of N-fixing tree species on the biomass and structure of soil microbial community of the second rotation Eucalyptus plantations in subtropical China, The phospholipid fatty acid (PLFA) analysis was used to quantify the microbial community biomass and composition in Eucalyptus urophylla monoculture forest and a mixed Eucalyptus urophylla and Dalbergia odorifera forest on dry and wet season. The results showed that the soil organic carbon content, NH₄-N, NO₃-N, TN, and litter biomass in mixed forest were significantly higher by 17.77%, 41.62%, 85.59%, 25.38%, 19.12% compared with that in monoculture forest at 0~10 cm depth except soil carbon content. Also in the mixed forest, the bacterial community biomass significantly increased, but the fungal community biomass was significantly reduced. Likewise, the relative abundances of total bacterial community, Gram-positive bacterial communities were significantly increased in dry season, but the relative abundance of fungal communities were significantly declined. No significant difference was found in the relative abundance of other microbial communities between the two forests in wet season, except the total bacteria. The results of principal component analysis (PCA) showed that the soil microbial community structure in mixed forest was clearly separated from the monoculture forest on the PC2 axis (p<0.05). This difference was caused mainly by the relatively higher abundances of bacteria and the relative lower abundances of fungi in mixed forest. Redundancy analysis (RDA) showed that litter biomass, C/N (litter), NH₄-N, and TOC were the dominant factors driving the changes of soil microbial community composition of the second rotation Eucalyptus plantations in subtropical China. In addiction, the trench experiment showed that the root and root secreting labile material may be the important sources of microbial biomass carbon in the second rotation Eucalyptus plantations.