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气候变化对土壤有机碳库分子结构特征与稳定性影响研究进展
张仲胜, 李 敏, 宋晓林, 薛振山, 吕宪国, 姜 明, 武海涛, 王雪宏
中国科学院东北地理与农业生态研究所
摘要:
气候变化与土壤碳库之间的相互作用及耦合机制一直是学术界研究的热点与难点。虽然目前在群落-生态系统、区域-全球等不同尺度上开展了大量研究,然而在分子尺度上探究气候因子波动对土壤有机碳库化学结构特征影响机制方面却鲜有研究。本文综述了近年来气候因子变化及其导致的环境、生态因子变化与土壤有机碳库分子结构特征的关系。气温升高不仅将改变土壤中源自植物部分的有机碳来源特征,同时也会将加速土壤木质素等碳组分分解,排水或者旱化引起有机质分解加速,土壤中C=O键增加。植被演替、土壤动物及微生物等与气候变化密的切相关的生态因子则会影响输入土壤植被残体性质,加速糖类、脂类及木质素分解、并改变有机碳结构的生物分子标志物;土壤中有机碳稳定性与分子结构特征密切相关,土壤中具有高的苯环结构(芳香族化合物)及O-烷基碳通常表明土壤碳库具有更高的稳定性,而之前认为较为稳定的木质素等结构在气候变暖背景下可能并不稳定。未来研究中应着重关注与土壤有机碳分子标志物的识别与生态意义判读、生物对土壤有机碳分子结构转换过程的调控作用及机制、大尺度环境/生态过程与碳库分子结构转变的耦合机制及新的土壤有机碳分子结构辨识技术及判读等方面的研究。
关键词:  气候变化  土壤碳库  分子结构  稳定性
DOI:10.11766/trxb201707240324
分类号:
基金项目:国家重点研发计划项目(2017YFC0505901、2016YFC0500404)和国家自然科学基金项目(41471081,41671081)
Effects of Climate Change on Molecular Structure and Stability of Soil Carbon Pool: A General Review
ZHANG Zhongsheng, LI Min, SONG Xiaolin, XUE Zhenshan, LÜ Xianguo, JIANG Ming, WU Haitao, WANG Xuehong
Northeast Institute of Geography and Agroecology, Chinese Academy of Sciences
Abstract:
Soil generally serves as both sink and source for atmospheric CO2, and plays a crucial role in maintaining carbon balance on the global scale, and mitigating the greenhouse effect. Mechanisms for interaction and combination between climate change and soil carbon pool have long been a hot spot and a hard nut to crack for the academic circle. Although extensive studies have been done on the subject at community-ecosystem, and regional-global scales, little has been reported about mechanisms of the variation of climate factors affecting chemical structure of the soil organic carbon pool (SOC) at the molecular scale. This review summarizes recent works on changes in climate factors and the changes in environmental and ecological factors they trigger and their relationships with molecular structure of the soil organic carbon pool. Climate warming not only changes characteristics of the sources of SOC from plant tissues, and significantly increases the content of cutin, a component of leaf epidermis, but also keeps relatively unchanged or declining the major components of SOC, such as carbohydrate, lignin, suberin and the like. Meanwhile, warming also accelerates decomposition of lignin and some other carbon components, promotes decomposition of aliphatic compounds, cutin and cyclic compounds and enhances soil microbiota in activity, thus leading to accumulation of plant-sourced alkyl-structured and/or microbe-sourced organic matter. Changes in soil hydrological regime also alter characteristics of the functional groups of soil organic carbon. For instance, drainage or drought triggers acceleration of decomposition of organic matter mineralization, thus increasing C=O bonds in soil; and fluctuation of soil water table controls chemical structure of the organic matter by affecting Fe form in the soil. Vegetation succession changes sources of soil organic matter due to difference between plant residues in inherent resistance to decomposition, and consequently alters properties of the soil organic carbon in the end. In the same climate zone, soils covered with various predominant vegetations are often characterized by remarkable differences in molecular structure of soil organic matter. Soil fauna and microorganisms, which are both ecological factors closely related to climate change, also alter properties of the plant residues in soil, promote decomposition of lipids, lignin and saccharides, and form different biomarkers. However, still not much has been done on how soil fauna and microbes alter molecular structure of soil organic matter. Stability of SOC is closely related to molecular structure of soil organic matter. Generally, SOC are more stable in the soil where contents of aromatic and O-alkyl compounds are high. In the soil the youngest fraction of carbon (formed in the past 107 years) usually features more aromatic compounds and low ratios of O-alkyl carbon to aromatic carbon, while the oldest fraction of carbon (over 1000 years) does less compounds and O-alkyl carbon. However, lignin is not so stable as previously expected facing climate warming. In the future, more researches should be done with stresses on special biomarkers and their ecological meaning, effect and mechanism of biota regulating molecular transformation processes of SOC, combined mechanisms of large-scaled environmental/ecological process and transformation of molecular structure of the carbon pool, and techniques to identify and interpret new molecular structures of SOC.
Key words:  Climate change  Soil carbon pool  Molecular structure  Stability