中速周转碳库的温度敏感性

Temperature is one of the most important variables in controlling and influencing the decomposition rate of soil organic carbon. Hence, the response of soil organic carbon pools to globally rising surface temperature crucially determines the feedback strength between global climate change and the global carbon cycle. The temperature sensitivity of decadally cycling soil carbon, the main component of soil organic carbon pools, becomes a focal point in current global change research. This proposed project will address this key issue by carrying out a 2-year incubation experiment using unique soils, a 13C natural tracer method, and a recently improved CO2-trapping and 13C-analysis techniques. We will use three soils from long-term (23, 33 and 55 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 soils from two long-term bare fallow and nearby old field sites for testing the temperature sensitivities of annually cycling and decadally cycling soil carbon pools. This experimental setting will enable us to uniquely clarify the recent controversy concerning temperature sensitivities of different soil carbon pools, and to constrain the temperature sensitivity of decadally cycling soil carbon pools with different ages. Our 2-year incubation experiment will also permit us to investigate the temporal dynamics of soil organic carbon decomposition and its temperature sensitivity. The operating mechanisms behind the temperature responses will be critically addressed by analyzing the influences of biotic and abiotic factors involved in the experiment.

温度是影响和控制土壤碳库矿化的关键因子，温度升高与土壤碳库之间的关系在很大程度上决定未来全球碳循环和温度变化之间的反馈关系。中速周转土壤碳库（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之一。但是，受方法学限制，目前结果争议很大。本项目以中速周转土壤碳库为研究对象，在不同温度下对长期C3-C4植被转变试验及长期裸地休闲(中速周转碳)和撂荒（快速周转）试验处理土壤进行室内长期培养实验，借助天然13C同位素示踪法区分不同周转速率碳库组分，同时采用自主改进的动态碱液吸收技术精确量化土壤呼吸CO2和13C同位素丰度，探明中速周转、快速周转土壤碳库的温度敏感性及其随培养时间的变化幅度，解析生物和非生物因素对中速周转碳库温度敏感性的影响机理，研究结果将有助于澄清不同土壤碳库温度敏感性的争论，为确定全球气候变化与土壤碳循环间的反馈关系提供新的思路。

温度是影响和控制土壤碳库矿化的关键因子，温度升高与土壤碳库之间的关系在很大程度上决定未来全球碳循环和温度变化之间的反馈关系。中速周转土壤碳库是土壤碳库的主体，其温度敏感性和激发效应是目前全球变化研究的核心问题。为此，项目组开展了深入的试验研究，获得新证据和新进展。（1）通过对两种C3-C4植被转变土壤进行360天培养，创新性的采用三种计算方法（Equal-C、Equal-time、First-order fitting），证实了中速周转碳库的矿化速率比快速周转碳库的矿化速率对温度变化更敏感，从而澄清了不同土壤碳库温度敏感性的争论，为确定全球气候变化与土壤碳循环间的反馈关系作出了贡献。（2）中速和快速周转碳库的碳释放随培养时间延长具有动态差异性。通过测定两种C3-C4植被转变土壤中的水溶性有机碳(DOC)、微生物量碳(MBC)、土壤有机碳含量(SOC)和δ13C，发现培养过程中DOC、MBC、SOC 含量随培养时间延长和升温呈下降趋势，MBC的δ13C值随培养时间延长呈先升高后下降趋势，土壤呼吸CO2的δ13C随培养时间延长而下降。（3）通过长达815天的室内培养试验，我们观测到玉米叶添加对土壤有机碳矿化的激发效应可分为三个阶段，即初期较强的负激发效应、中期为脉冲式的正激发效应和后期较为稳定而低水平的正激发效应。该结果明确了研究激发效应长期动态趋势的重要性。