基于高频协同观测的土壤CO2、CH4、N2O通量变化耦联关系及解耦机制研究

The process of soil CO2, CH4 and N2O flux is a hot topic in the field of climate change research. At present, there is already a deep understanding of the single greenhouse gas flux and the environmental regulation mechanism. The ecological system management programme selected based on a single greenhouse gas emission mechanism may cause the increase of the other two kinds of gas emissions. To avoid this, the relationship between the three gas fluxes, namely the coupling relationship, should be studied. There are obvious differences in meteorology and soil conditions between Changbaishan and Dinghushan forest ecosystem. In this study, we will take these two ecosystems as examples to obtain high-frequency flux data using soil greenhouse gases automatic multi-channel continuous monitoring system. Taking correlation coefficient as an indicator of the coupling relationship, we will analyze the dynamic changes of the coupling relationship on different time scales, summarizes the environmental conditions when coupling and decoupling occur, and identifies the integrated regulation mechanism of coupling/decoupling of moisture, temperature and soil parameters. Using pot experiment in lab, explores the carbon and nitrogen cycle processes and mechanism underlying the flux coupling and decoupling. Study on the coupling relationship between fluxes is an enrichment of the mechanism of carbon and nitrogen cycle. Moreover, it can provide theoretical support for the trade-off management to reduce the total emissions of the three greenhouse gases.

土壤CO2、CH4、N2O通量过程机理是气候变化的热点研究领域。目前对单种温室气体排放的过程机理已形成较为深入的认识。但仅基于单种温室气体排放机理选择的生态系统管理方法，可能导致其他两种气体排放量升高。为避免这一点，需要研究三种温室气体通量间关系即耦联关系。长白山与鼎湖山森林生态系统的气象及土壤等条件具有明显差异，本研究将以这两个生态系统为例，利用土壤温室气体全自动多通道连续监测系统获取高频通量数据，以土壤通量间相关系数作为耦联关系的指示性指标，揭示通量间耦联关系在不同时间尺度上的动态变化；归纳发生耦联与解耦时的环境条件；辨析水热、土壤等环境条件对耦联/解耦的综合调控机制；结合控制实验，探讨引起耦联与解耦的碳氮循环过程机制。对通量间耦联关系的研究，既是对碳氮循环过程机理的丰富；也可为制定减少三种温室气体总排放的权衡式管理措施提供理论支撑。

对不同土壤温室气体通量间的耦联关系研究，可用于指导生态系统温室气体减排增汇的权衡式管理，为应对全球气候变暖及碳中和目标的实现提供科学支撑。本项目基于两个典型森林生态系统的温室气体通量高频观测数据，分析了不同类型森林生态系统的土壤呼吸和CH4通量在日尺度上与季节尺度上的相关性及其对环境的响应，并结合多源数据收集，将在典型生态系统中发现的规律在区域尺度上进行了进一步地验证。结果显示，土壤CH4日通量与土壤呼吸日通量的比值在温暖季节高于寒冷季节，温带森林的比值平均为-0.56×10-3±0.01×10-3，亚热带森林的比值平均为-0.27×10-3±0.01×10-3；日尺度上，土壤CH4通量与土壤呼吸通量的相关性存在显著正相关（耦联）、显著负相关（耦联）和不相关（解耦）三种关系，其中以显著负相关为主，平均占比79%；温带森林在夏季发生通量间解耦的频次较高，亚热带森林在冬季发生解耦的频次较高。在季节尺度上，温带森林土壤CH4年均通量与土壤呼吸年均通量的比值为-0.48×10-3，亚热带森林为-0.15×10-3；两个生态系统的土壤CH4通量与土壤呼吸通量在季节尺度上均呈现为显著负相关。针对通量间相关性和环境条件的关系分析，发现了土壤CH4通量和土壤呼吸通量耦联/解耦的温度调控机制，土壤CH4日通量与土壤呼吸日通量的比值对温度的响应具有明显的分段现象，土壤CH4通量和土壤呼吸通量之间存在不对等的耦联关系，温度升高会减弱土壤吸收CH4对排放CO2的抵消作用，这意味着全球变暖背景下，增温驱动土壤吸收CH4和排放CO2两个过程的非等量耦联变化，增加土壤温室气体通量的总增温效应，并且增温可能通过引发CH4和CO2通量的解耦增加生态系统土壤温室气体通量评估的不确定性。