滨海芦苇湿地根际土壤有机碳输入和分解对模拟增温的响应机理

Rhizosphere is the most active and important area of soil carbon cycle in terrestrial ecosystems. To elucidate the variations of soil organic carbon input and decomposition in rhizosphere soil under warming condition is crucial for understanding the relationship between soil carbon cycle and climate change. Coastal wetlands have significant carbon sink function, where root-derived organic carbon is the most important source of soil carbon. However, presently in coastal wetland, the synchronous changes of a series of carbon processes mediated by root and rhizosphere microorganisms and the underlying mechanisms that they affect soil carbon balance under warming condition are not clear. In this project, Phragmites wetland in Yangtze estuary will be taken as the research object, open top chambers (OTC) will be used to realize in-situ simulated warming. Besides, a series of field and laboratory methods (such as minirhizotron method, in situ root exudates collection method, phospholipid fatty acid (PLFAs) method and high-throughput sequencing technology) will be integratedly adopted. In the coastal Phragmites wetland, the effects of air warming on organic carbon input and decomposition in rhizosphere soil will be clarified through the simultaneous observations of root dynamic, root exudates and rhizosphere microbial activity and composition. After then, the response mechanism of organic carbon input and decomposition in rhizosphere soil to air warming will be revealed through quantitative analyses of the relationships among root, root exudates and rhizosphere microorganisms, as well as their relationships with environmental factors in rhizosphere soil and aboveground growth indicators.

根际是陆地生态系统土壤碳循环中最为活跃和重要的区域，阐明升温条件下根际土壤有机碳输入和分解的变化规律对于理解土壤碳循环与气候变化的相互关系具有关键作用。滨海湿地碳汇功能显著，根源有机碳是其土壤碳的最主要来源。但目前对升温条件下滨海湿地由根系和根际微生物介导的根际土壤碳过程的同步变化及其影响土壤碳平衡的内在机理并不清楚。本项目以长江口芦苇湿地为对象，利用开顶式生长箱（OTC）进行原位模拟增温，并集成微根管法、原位根系分泌物收集法、磷脂脂肪酸（PLFAs）法和高通量测序技术等野外和室内试验手段。通过对根系动态、根系分泌物及根际微生物活性和组成的连续同步观测，阐明气温升高对滨海芦苇湿地根际土壤有机碳输入和分解的影响。通过对根系、根系分泌物和根际微生物相互之间，及其分别与根际土壤环境因子和地上部分生长指标的定量关系分析，在生态系统水平上揭示滨海芦苇湿地根际土壤有机碳输入和分解对气温升高的响应机理。

目前关于增温条件下滨海湿地根系和根际微生物介导的碳过程与根际碳收支关系的认识有限，很大程度上制约了关于滨海湿地土壤碳循环对全球气候变化响应和反馈的认知。本项目以长江口崇明东滩芦苇湿地为对象，结合野外原位增温与多种室内试验，重点研究气温升高背景下芦苇湿地表层土壤根系（直径≤２ｍｍ细根）生长、周转和根系分泌物的动态特征，根际微生物活性、多度和组成的响应规律，揭示根系和根际微生物的交互作用影响根际碳收支的内在机理。主要研究结果如下：①两年的连续增温显著提高了芦苇湿地0—10cm土层总有机碳含量，而这主要是由于惰性碳的积累导致的；②增温在第一年显著提高了芦苇湿地0—20cm土层细根的总量和生长速率；这种促进作用第二年在0—10cm表层更加显著，但在10—20cm土层有所减弱；③增温条件下芦苇湿地细根的周转速率未发生显著变化，但由于增温提高了现存生物量，致使细根周转碳输入量显著增加；④增温显著增加了芦苇湿地0—20cm土层的根系分泌物分泌速率，但增幅有限，根系分泌物碳输入的显著增加仍主要源于更高的细根生物量；⑤增温对芦苇湿地表层土壤微生物的活性、多度和α多样性影响不显著，但在一定程度上改变了细菌和真菌群落的结构组成和优势种群，这可能主要是因为根际微生物偏好利用高碳氮比的根系分泌物输入有机碳，导致根际激发效应不明显。⑥经过两年的连续增温，芦苇湿地表层土壤细根周转碳输入和根系分泌物碳输入同时增加，而根际微生物有机碳分解碳输出变化不显著，从而使其表现出明显的净碳输入和有机碳累积。上述前沿性基础研究工作丰富了对气候变化条件下滨海湿地根际碳过程的潜在响应及其影响土壤碳循环内在机理的科学认知，填补了相关领域的研究空白，具有较高的学术价值。依托本项目目前共发表研究论文7篇，其中SCI论文5篇，获得实用新型专利2项，另有多项研究成果正在整理和撰稿中。