土壤微生物群落结构对中亚热带三种典型阔叶树种凋落物分解过程的响应

Response of soil microbial community structure to the leaf litter decomposition of three typical broadleaf species in mid-subtropical area,southern China

通过小盆模拟试验研究了南方红壤丘陵区典型阔叶树种香樟、白栎和青冈的凋落物分解过程中土壤微生物群落结构的异同。结果表明:(1)凋落物含氮量:白栎>香樟>青冈;碳、木质素的含量以及碳/氮比、木质素/氮比:青冈>香樟>白栎;分解速率:白栎>香樟>青冈;(2)随着凋落物分解的进程,土壤微生物群落16∶0、15∶0、i16∶0、a17∶0、17∶0、18∶2ω6,9c和10Me18∶0的含量上升,18∶0、14∶0、16∶1ω7c、18∶1ω7c、cy19∶0、i19∶0和10Me19∶0的含量下降,饱和直链脂肪酸/单不饱和脂肪酸、革兰氏阳性菌/革兰氏阴性菌以及cy19∶0/18∶1ω7c的比值都显著上升。(3)两个时期白栎凋落物处理土壤16∶0、15∶0、a15∶0、i16∶0、a17∶0、17∶0、cy19∶0、18∶2ω6,9c、18∶1ω9c和10Me18∶0的含量显著高于香樟和青冈凋落物处理的土壤,细菌、真菌的磷脂脂肪酸含量以及磷脂脂肪酸总量显著高于香樟和青冈凋落物处理的土壤。随着阔叶凋落物的分解,变化的土壤环境对土壤微生物群落的胁迫增强,土壤微生物群落结构发生显著变化。与香樟和青冈的凋落物相比,白栎凋落物碳/氮比和木质素/氮比低、分解快,能显著改善土壤微生物群落结构,更有利于土壤肥力提高和生态系统养分循环的改善。

Litters are the important component of forest ecosystem and play a key role in ecosystem nutrient cycle. The mineralization of nitrogen, phosphorus and other nutrients from plant litters provides an important input of inorganic nutrients to the soil, which can be taken up by plants. Soil microbial communities are one of the important factors controlling the dynamics of nutrient mineralization or immobilization during decomposition. However, different litters have different impacts on soil microbial communities. To understand the responses of soil microbial community composition to different litter decomposition, the PLFAs （phospholipid fatty acids） compositions of the soil microbial communities under three typical broadleaf species treatments, including camphor tree （ Cinnamomum camphora） , white oak （ Quercus fabri） and blue Japanese oak （ Cyclobalanopsis glauca） were studied by the simulation experiment with flowerpots at the Ecological Benefit Monitoring Station of the Yangtze River Protection Forest, which is located in Hengyang County of southern Hunan Province. The results showed that ： （ 1 ） the initial nitrogen content of three broadleaf litters ranked as follows ： white oak 〉 camphor tree 〉blue Japanese oak, however the initial content of carbon and lignin, and the carbon-nitrogen ratio, ligninnitrogen ratio had inverse trend： blue Japanese oak 〉camphor tree 〉white oak. And the white oak litter had the highest decomposition rate, followed by camphor tree and blue Japanese oak. （2） During litter decomposition, the PLFAscompositions of the soil microbial communities under three litter treatments had similar tendency： the concentrations of 18：0, 14：0, 16：lto7c, 18 ：lto7c, cyl9：0, i19：0 and 10Mel9：0 decreased gradually, and the concentrations of 16：0, 15：0, i16：0, a17：0, 17：0, 18：2ψ6,9c and 10Mel8：0 increased step by step. Three stress indicators, the saturated PLFA to monosaturated PLFA ratio （SAT/MONO）, the Gram-positive bacteria to Gram-positive bacteria ratio （G^＋/G^-） and the cyl9：0/18：1to7c ratio of the soil microbial community increased significantly with the decomposition of three kind of litters. （3） The concentrations of 16：0, 15：0, alS：0, i16：0, a17：0, 17：0, cyl9：0, 18：2ψ6,9c, 18：lψ9c and 10MelS：0, the PLFA of bacteria and fungi and the total PLFA of microbial community in soils treated with white oak litters were significantly higher than those of camphor tree and blue Japanese oak during the two periods. The soil microbial community structure changed significantly during the decomposition of broadleaf litters. Comparing with camphor tree litter and blue Japanese oak litter, the litters of white oak had lower carbon-nitrogen ratio, lignin-nitrogen ratio, and decomposed more quickly, which improved the soil microbial community structure significantly. Our results suggested that white oak litter was more suitable for soil fertility improvement and the nutrient cycle in forest ecosystem, comparing with camphor tree litter and blue Japanese oak litter.