亚热带森林叶片和细根凋落物分解的主场优势效应及其驱动机制研究

Biological decomposition of detritus is a critical ecosystem function that regulates ecosystem nutrient and carbon cycles. Full knowledge of the influence of biotic and abiotic factors on the pathways of litter decay in forests is essential in understanding biogeochemical cycle of forest ecosystem responses to biodiversity loss and climate change. Litter derived from the plants growing above or near the plant (home) decomposes more quickly than when placed far from its plant of origin (away), which has been termed home field advantage of litter decomposition. Most of the previous studies only considered leaf litter decomposition when testing the generality of home field advantage, and the temporal patterns of home field advantage remains unclear. Specialization of soil biota to decompose the litter that they encounter most often has been considered as the main mechanism to explain home field advantage. However, there is little direct evidence supporting this hypothesis, and the relative role of soil animal and microorganism in driving the home field advantage is unknown. The overall objective of this project is to examine the generality of home field advantage, and provide the necessary mechanistic understanding of home field advantage of litter decomposition, thus helping to optimize and improve the predictive power of decomposition models. To be specific, we will use litter translocation experiment to answer the following questions: (1) Does home field advantage occur during leaf litter and fine root decomposition in subtropical forest? (2) How does home field advantage vary over time? (3) What is the role of soil animal and microorganism in driving the home field advantage?

生物对凋落物的分解作用是重要的生态系统功能，对生态系统营养和碳循环有重要影响。充分认识生物和非生物因子对凋落物分解速率的影响是预测生物地球化学循环对全球变化响应的关键。凋落物在其原生地分解的速率比在非原生地分解的速率更快的现象被称为凋落物分解的主场优势效应。目前对主场优势效应是否普遍存在及其驱动机制还存在较大争议。已有研究主要以叶片凋落物为对象开展主场优势效应研究，对主场优势效应随分解时间的变化格局很少有报道。土壤生物的特化作用被认为是主场优势效应的驱动机制，然而目前还缺乏直接的证据。本研究拟通过3种森林凋落物的移置实验，回答以下问题：（1）叶片与细根凋落物分解是否表现主场优势效应？（2）主场优势效应随时间的变化格局是什么？（3）土壤动物和微生物对主场优势效应的驱动作用。本研究的目的是检验主场优势效应的普遍性，探讨主场优势效应的可能驱动机制。研究结果对优化凋落物分解过程模型有重要意义。

越来越多的研究发现凋落物在其原生地分解的速率比在非原生地分解的速率更快，这个现象被称为凋落物分解的“主场优势效应”。土壤中的分解者特化通常被认为是主场优势效应形成的主要原因，但至今为止，到底是哪一类土壤生物驱动了凋落物分解的主场优势效应还不清楚。本项目通过甜槠、杉木和毛竹凋落物的完全置换分解实验，研究了这三种植物凋落物的主场优势效应强度，分析了土壤动物和微生物在此过程中的相对重要性。结果表明最难分解的甜槠凋落物和最易分解的毛竹凋落物均表现出了主场优势效应，但杉木凋落物没有出现该现象。土壤动物参与与否没有明显的改变凋落物分解主场优势效应的格局，说明驱动主场优势效应的是微生物类群而不是土壤动物。分析凋落物上的细菌群落发现，细菌群落受到凋落物类型的影响，但不受分解场地的影响；但是真菌群落则不仅受到凋落物类型的影响，同时凋落物的类型与分解场地的交互作用也显著的影响了真菌的群落结构，这主要是因为甜槠和毛竹上的真菌群落受到其分解场地的显著影响。因此真菌很可能是甜槠和毛竹凋落物分解出现主场优势效应的主要驱动者。在全球环境变化和土壤利用变化的背景下，真菌分解者与其最常分解的凋落物之间的分离将可能影响陆地生态系统的碳和养分循环。