模拟氮沉降和灌草去除对杉木人工林地土壤微生物群落结构的影响

土壤微生物是陆地生态系统重要的分解者和地上-地下相互作用的纽带。本文以亚热带杉木(Cunninghamia lanceolateata)人工林为对象, 通过模拟林冠层氮沉降和林下灌草去除, 设置4种处理, 包括: 对照(CK)、灌草去除(UR)、氮沉降(N)和氮沉降加灌草去除(N × UR)的野外控制实验, 研究土壤微生物群落结构的响应。本实验分别于2016年4月(春季)和10月(秋季)采集0-10 cm层土壤样品, 运用磷脂脂肪酸法(PLFAs)分析土壤微生物群落结构。结果表明: (1) 10月份土壤微生物总PLFAs量及其他类群土壤微生物PLFAs量显著高于4月份(P < 0.05), 真菌/细菌比值没有显著差异。土壤微生物PLFAs中细菌占优势, 其次为真菌, 放线菌的占比最小; (2)相比CK处理, UR处理下土壤微生物总PLFAs量、细菌PLFAs量、革兰氏阴性菌PLFAs量和放线菌PLFAs量有增加趋势, 但未达到显著差异水平(P > 0.05); (3)相对CK, UR、N和N × UR处理降低了4月份土壤微生物多样性(H°)和均匀度指数(J), 但提高了10月份土壤微生物多样性指数; (4)冗余分析表明, 土壤硝态氮和总磷含量与土壤微生物群落之间呈现显著相关。本研究表明土壤微生物PLFAs在各处理下都表现出明显的季节动态; 短期内林下灌草去除对土壤微生物PLFAs影响表现出一定的促进作用, 氮沉降对土壤微生物群落影响还不甚明显, 需要长期的监测研究来评估两者及其交互作用对土壤微生物群落及其功能的影响。

Assessing influence of simulated canopy nitrogen deposition and understory removal on soil microbial community structure in a Cunninghamia lanceolata plantation

Soil microorganisms have been recognized as important decomposers that link above- and below-ground processes in terrestrial ecosystems. In this study, we conducted an experiment to assess the influence of canopy nitrogen deposition and understory removal in a Cunninghamia lanceolata plantation. The effects of four treatments, i.e. control (CK), understory removal (UR), nitrogen deposition (N) and nitrogen deposition plus understory removal (N × UR) on soil microbial community were investigated using phospholipid fatty acids (PLFAs). Soil samples (0-10 layer) were collected in April (spring) and October (autumn), 2016. Results showed that the total soil microbial PLFAs and the other groups (bacteria, fungi and actinomycete) of soil microbial PLFAs in autumn were significantly higher than those in spring, but fungi/bacteria ratio did not change significantly between two sampling seasons. Bacteria dominated among different PLFAs groups, followed by fungi and actinomycetes. Relative to CK treatment, UR treatment had slightly higher total PLFAs, bacterial PLFAs, gram negative bacterial PLFAs and actinomycetes PLFAs although not significant at 0.05 level. Shannon-Wiener and Pielou indices of UR, N and N × UR treatments decreased in April whereas Shannon-Wiener index was higher in October. Soil nitrate nitrogen and total phosphorus were significantly correlated with soil microbial community based on redundancy analysis. No significant effect of nitrogen deposition was observed probably due to the short period of study. But understory removal seems to promote the impact of nitrogen deposition. Seasonal variations were detected in this study suggesting that long-term experiments are required to explore the continuing effects of environmental changes on soil microbial communities and their functions.