土壤干湿循环过程控制中速周转碳库分解温度敏感性的关键机制研究

The process of the soil drought and subsequent rewetting cycles caused by the precipitation changes is a key link controlling the temperature sensitivity of soil organic carbon decomposition, which decides the feedback between the global carbon cycle and climate warming. Decadally cycling soil organic carbon is the main component of soil organic carbon pools. The temperature sensitivity of decadally cycling soil organic carbon becomes a focal point in current global change research. Debates still exist because of the methodology restricted. This proposed project will address this vital issue by carrying out a 3-year incubation experiment using unique soils under simulated temperature and moisture regimes, a 13C natural tracer method, and a recently improved continuous CO2-trapping and 13C-analysis techniques. We will use two soils from long-term (23 and 33 years) C3-C4 vegetation switch sites for their unique 13C tracers which will allow us to separately test the temperature sensitivities of annually cycling and decadally cycling soil carbon pools. We will also use four soils from long-term bare fallow field sites for testing the temperature sensitivities of annually cycling and decadally cycling soil carbon. This experimental setting will enable us to uniquely clarify the mechanism of the drought and subsequent rewetting cycles controlling the temperature sensitivity of decadally cycling soil carbon. Our 3-year incubation experiment will also permit us to investigate the temporal dynamics of decadally and annually cycling soil carbon and their temperature sensitivity. The mechanisms behind the temperature responses will be critically addressed by analyzing some impact factors, such as substrate availability, soil physical protection, microbial community composition and enzymatic activity. It will provide a scientific basis for further determining the feedback between climate change and global carbon cycle.

降水导致的土壤干湿循环过程是控制土壤有机碳分解温度敏感性的关键环节，决定了未来全球碳循环和气候变暖之间的反馈关系。中速周转碳库(decadally cycling C)是土壤碳库的主体，其温度敏感性是目前全球变化研究的核心问题。但受方法学限制，存在较大争论。本项目以土壤中速周转碳库为研究对象，在不同温度下对C3-C4植被转变土壤、长期裸地休闲（中速周转碳库）和撂荒试验处理（相对快速周转碳库）土壤进行长期培养，模拟土壤干湿循环过程，借助天然13C同位素示踪法区分中速、快速周转碳库，采用自主改进的连续动态碱液吸收系统精确量化土壤呼吸CO2和δ13C丰度，分析土壤中速、快速周转碳库的温度敏感性及其长期变化动态，解析底物有效性、土壤物理化学保护、微生物群落组成和酶活性等影响因素，揭示土壤干湿循环过程控制中速周转碳库温度敏感性的内在机制，为确定全球气候变化与土壤碳循环之间的反馈关系提供科学依据。

全球气候可能会显著增加陆地生态系统的干湿循环(drying-rewetting cycle, DWC)。土壤干湿循环过程是控制土壤有机碳分解温度敏感性的关键环节，决定了未来全球碳循环和气候变暖之间的反馈关系。干旱通常会降低土壤微生物的活性，减少活性底物的扩散，减弱土壤呼吸。而重新湿润可能进剩余的耐DWC胁迫的微生物同化容易获得的底物并导致土壤迅速释放大量CO2（Birch effect）, 中速周转碳库(decadally cycling C)是土壤碳库的主体，其温度敏感性是目前全球变化研究的核心问题。但受方法学限制，存在较大争论。本项目以土壤中速周转碳库为研究对象，在不同温度下对C3-C4植被转变土壤、长期裸地休闲（中速周转碳库,dSOC）和撂荒试验处理（相对快速周转碳库,aSOC）土壤进行长期培养，模拟土壤干湿循环过程，借助天然13C同位素示踪法区分中速、快速周转碳库，采用自主改进的连续动态碱液吸收系统精确量化土壤呼吸CO2和δ13C丰度，分析土壤中速、快速周转碳库的温度敏感性及其长期变化动态，解析底物有效性、土壤物理化学保护、微生物群落组成和酶活性等影响因素，揭示土壤干湿循环过程控制中速周转碳库温度敏感性的内在机制，为确定全球气候变化与土壤碳循环之间的反馈关系提供科学依据。 主要结果如下：.1. 在两种土壤中，dSOC的Q10始终大于aSOC，DWC使HA土壤tSOC、aSOC和dSOC的Q10分别降低41.89%、41.23%、43.45%，GZ土壤分别降低41.04%、43.05%和30.01%；.2. 土壤物理结构的破坏及不同组分碳库对干湿交替的响应程度不同是导致累积土壤呼吸随干湿交替次数增加而持续增加的可能原因；.3. 随着DWC数量的增加，越来越多的有机碳被转化为MBC而不是CO2，很好地解释Birch效应中复湿后CO2脉冲随时间下降的现象。我们的结果有助于理解陆地生态系统中土壤MBC和DOC对DWC的响应，并且可以改进对未来更多可变土壤水分状况下土壤碳排放的预测。