气候变暖条件下西南亚高山针叶林根系分泌物C:N化学计量特征与土壤C/N循环过程的耦合机制研究

The importance of root-derived labile C inputs on soil processes and functions and their feedbacks to climate change has increasingly been recognized. However, only limited effort has been made to examine the potential mehanisms by which root exudation, especially for root exudation stoichiometry, influence soil ecological processes under global warming through their effects on C-nutrient cycling, which greatly limits our understanding of root-soil-microbe interactions and their potential ecological consequences on forest ecosystem functions. In this study, we employ a suite of novel experimental methods to detremine, quantitatively and qualitatively, slouble root exudates, exudate stoichiometry (C: N), and their biogeochemical consequeces on forest soil C-nutrient cycling under experimental warming in subalpine spruce plantation in the eastern Tibetan Plateau. Meanwhile, we also investigated the physicochemical changes of mineral-organic associations interface, soil microbes and extracellular enzyme activities closely related to these processes in the field. Our goals are to 1) quantify the effects of experimental warming on root exudation fluxes (g C m-2 year-1) at ecosystem scale, chemical composition and C: N stoichiometry in field-grown trees, 2) explore the coupling relationships between exudate stoichiometry and rhizosphere soil C-N cycle under experimental warming, 3) validate and quantify the relative contribution of direct microbial metabolic and indirect abiotic mechanism on rhizosphere priming effects induced by root exudate. Our proposal will greatly advance and deepen the development of rhizosphere ecological processes and associated regulation mechanism in response to changing environmental conditions.

目前，有关气候变化下森林根系分泌物输入（尤其是化学组分变化）与土壤生态过程耦合效应的原位研究十分缺乏，严重制约了对根系-土壤-微生物互作机制及其对环境变化响应的深入认识。本项目以亚高山人工云杉林为对象，以根际过程为切入点，以根系分泌物为核心，采用红外辐射增温，结合树皮环割和林下分泌物添加试验，重点研究增温对亚高山森林根系分泌物速率、化学组成及其介导的土壤C-N循环过程的影响，并同步监测土壤微生物特性与矿物-有机物复合体物理化学界面特征变化，旨在：1）刻画气候变暖下森林在生态系统尺度上根系分泌物输入通量、化学成分及其伴随的C:N化学计量特征；2）揭示森林根系分泌物C:N化学计量特征与土壤C-养分循环过程的偶联效应及其对增温的响应；3）厘定微生物与非生物作用过程对根系分泌物诱导的土壤C/N循环激发效应的影响及其相对贡献。本项目实施可提升森林根际生态过程的调控机理及其对环境变化响应的认知水平。

目前关于全球气候变化下森林根系分泌物输入（尤其是化学组分变化）与土壤生态过程耦合效应研究和认识有限，很大程度上制约了森林根际理论体系发展及其生态重要性的科学认知。本项目以西南亚高山针叶林为对象，通过野外原位试验与室内控制试验相结合，重点研究增温背景下亚高山针叶林根系分泌物输入特征及其所驱动的土壤过程及其生态反馈效应。主要研究结果如下：①推进和完善了森林根际研究技术体系，获得根际技术国家专利3项，为更深入揭示根系分泌物生态效应与作用机制提供了技术支撑；②从根际这一独特视角，独辟蹊径地破译了高寒森林生长与生产力稳定的根际养分维持机制“密码”；③发现根际过程降低N沉降下高寒生态系统土壤固碳潜力（根际碳源/非根际碳汇）；④发现根系分泌物介导的养分获取策略是维持森林不同物种共存的重要调控途径；⑤揭示了外生菌根主导的高山针叶林根系多维经济谱特征。在此基础上，项目负责人对森林根系分泌物研究技术体系与国际前沿动态进行了系统性概括与总结。上述前沿性基础研究工作丰富和拓展了森林根际生态过程及其生态重要性的系统性认知，具有鲜明的特色和优势。依托本项目共发表研究论文18篇，其中SCI论文15篇（一区8篇，全部为TOP10%期刊），中文3篇，出版森林根系分泌物研究专著1部。