根际微生物群落特征影响亚热带森林细根分解的机理

Fine root decomposition plays an important role in terrestrial ecosystem carbon (C) and nutrient cycling. With development of research on the subjects of global C cycle and forest ecological system, fine root decomposition study had gained a widespread attention and became one of the hotspots in current research on forest C cycle. Fine root decomposition is regulated by both intrinsic factors and environmental factors. Among these factors, root chemical composition is the primary controller of root decomposition. The rhizosphere soil microbial community, as the main participant of root decay, is also one of the most important factors of fine root decomposition. The present study, 6 tree species (two coniferous species: Cunninghamia lanceolate and Pinus massoniana; two deciduous species: Liquidambar formosana and Choerospondias axillaris; two broadleaved evergreen species: Cyclobalanopsis glauca and Lithocarpus glaber) were selected to study the chemical composition change and decomposition process of fine roots in subtropical forests. By using litterbag method and carborundum tube method, the mechanism of how rhizosphere soil microbial community characteristics influence on fine roots decomposition will be clarified. Putting the fine roots and drying-rewetting soil together in the carborundum tube to clarify how soil microbial community characteristics affect the root decomposition process. Fine roots decomposition experiment with litterbag method was designed to test the hypothesis that the soil microbial community has a predilection towards the litter from their original site.

细根分解是陆地生态系统C和养分循环的重要组成部分，随着全球碳循环研究的开展和对森林生态系统研究的深入，细根分解的重要性得到了生态学界的广泛认同。细根分解过程受内在和环境因素的复杂影响，细根的化学组成是细根分解最主要的影响因子，而根际土壤微生物是细根的主要分解者，也是影响细根分解的重要因素。本项目选择6个树种（针叶树种杉木和马尾松、落叶树种枫香和南酸枣、常绿阔叶树种青冈和石砾）的细根，在明晰中亚热带森林不同树种细根的化学成分和分解动态基础上，着重研究了根际土壤微生物群落特征影响细根分解过程的作用机理。通过温室控制砂滤管法细根分解实验，封装不同树种的细根及风干-再湿润的土壤样品，明晰根际土壤微生物结构及功能影响不同化学成分细根分解过程的规律。采用分解袋法，将每个树种的细根样品在各自及其它树种林分同时进行分解实验，从新的实验角度验证"土壤微生物对其植物凋落物具有取食偏好"的假设。

细根分解是陆地生态系统C和养分循环的重要组成部分，细根分解的重要性得到了生态学界的广泛认同。细根分解过程受内在底物质量和环境因素的复杂影响，细根的化学组成是细根分解最主要的影响因子，而土壤微生物是细根的主要分解者，也是影响细根分解的重要因素。本项目选择6个树种（针叶树种杉木和马尾松、落叶树种枫香和南酸枣、常绿阔叶树种青冈和石砾）的细根，比较了细根化学成分和物理结构差异，采用分解袋法林地分解实验研究了细根及地上凋落物的分解动态，采用氯仿熏蒸法测定了不同林分土壤微生物生物量C、N及其季节变化，环境微生物群落多样性测序方法分析了不同林分土壤微生物群落结构及多样性，对进一步明晰土壤微生物群落结构影响细根分解过程的机理研究提供理论依据。.现有的主要研究结果有：① 6个树种细根的直径、根长、比根长、比表面积和组织密度具有很大的异质性，C/N随根序升高而增加。不同树种细根中养分及木质纤维素组分的含量存在差异，总的来说青冈细根的底物质量最低，而枫香的最高。②早期演替树种（马尾松、南酸枣和枫香）分解较快，演替后期的常绿阔叶树种（青冈、石栎）和杉木的分解较慢，分解180d后保留率也较高。细根底物质量中P和Ca含量是影响细根早期分解的主要因素，而N和木质素含量影响不大。6个树种凋落叶分解动态实验结果与细根分解的规律一致，分解常数之间也存在显著的对应关系。③ 4种森林土壤各土层MBC和MBN含量均以南酸枣落叶阔叶林最高，杉木人工林最低。MBC、MBN与土壤总有机碳、全氮、碱解氮含量之间存在极显著正相关（p<0.001），同时土壤MBC、MBN含量与土壤总C、N含量一起对土壤N转化速率影响显著。④腐殖层与矿质层细菌群落丰度差异不大，真菌群落丰度腐殖层显著大于矿质层，总的来说南酸枣样地土壤中的菌群丰度最大。腐殖层的土壤真菌与细菌群落多样性高于矿质层，南酸枣样地的土壤真菌与细菌群落多样性均为最高。