土壤有机碳矿化的"调节阀"学说与验证

It is essential to understand the process of soil organic carbon (SOC) mineralization as it is a fundamental process upon which all life ultimately depends. A central belief of soil microbiology is that the rate of mineralization of SOC is controlled by microbial activity. However, this does not explain the paradox of SOC mineralization, which is that even if 90% of the soil microorganisms are destroyed by CHCl3 fumigation, following fumigant removal, SOC mineralization continues at the same rate as in the undamaged soil. Recently, a new theory called the 'Regulatory Gate Hypothesis' was proposed to explain this phenomenon. It considers that mineralization of SOC is a two stage process: non-bioavailable, humified SOC is altered by abiological processes to bioavailable forms [K1]; the now bioavailable SOC is mineralised by the soil microbial biomass [K2]. However, there is insufficient evidence to support the 'Regulatory Gate Hypothesis'. Therefore, the abiotic release of SOC from soil, the changes in soil microbial populations due to CHCl3, and effect of soil perturbations and plant growth on abiotic and biotic release, respectively, will be determined in this project. Our aim is to obtain further evidence to support (or reject) the 'Regulatory Gate Hypothesis'. If identified as a key process, the 'Regulatory Gate Hypothesis' will greatly change our understanding of key SOC processes e.g. mineralization-immobilization, C sequestration and the modeling of soil processes, such as interactions between SOC and global warming.

土壤有机碳矿化是地球上所有生物赖以生存的关键过程，正确了解土壤有机碳矿化过程与作用机制具有重要意义。学界普遍认为土壤有机碳矿化速率受土壤微生物活性控制，然而该理论无法解释"土壤经氯仿熏蒸杀死大量微生物后仍以相同速率持续矿化"这一矛盾现象，对此，国际上提出一种 "调节阀"新学说（Regulatory Gate Hypothesis），认为土壤有机碳矿化包括非生物可利用有机碳向生物可利用有机碳的转化过程（K1）及生物可利用碳的微生物直接矿化过程（K2），但是，"调节阀"学说是否成立目前仍没有定论。因此，本项目将从土壤有机碳的非生物释放规律、熏蒸土壤微生物群落变化、土壤扰动和植物种植对生物与非生物碳释放的影响等方面深入研究，为证明或否证土壤有机碳矿化过程"调节阀"学说提供科学证据，研究结果将修正土壤有机碳矿化现有相关知识理论，有助于探明土壤有机碳与全球变暖交互作用等土壤复杂生物化学过程。

土壤有机碳矿化是地球碳循环的关键过程，正确了解土壤有机碳矿化过程与作用机制具有重要意义。学界普遍认为土壤有机碳矿化速率受土壤微生物活性控制，然而该理论无法解释氯仿熏蒸土壤中有机质矿化速率与不熏蒸土壤中有机质矿化速率一致的现象。有机质矿化的“调节阀”假说（Regulatory Gate Hypothesis）认为土壤有机碳矿化包括生物不可利用有机碳向生物可利用有机碳的转化过程（K1）及生物可利用碳的微生物矿化过程（K2），本项目”研究了土壤中ATP-微生物量的相关性、土壤有机碳矿化的非生物影响因素、熏蒸土壤微生物群落结构变化及熏蒸-梯度接种土壤中有机质矿化、微生物群落变化及其相关性。实验结果表明，好氧土壤中，微生物ATP含量与微生物量碳的比值关系较为稳定（7.9±2.24 μmol ATP g-1 SMBC），且不会随底物而变化；土壤在无菌条件下仍能以稳定、较低的速度产生DOC；熏蒸土壤土壤有机质矿化速率与土壤微生物大小、活性、群落结构不呈正相关关系，但前者受到物理扰动的影响；土壤熏蒸后微生物群落结构发生变化，对其接种新鲜土壤可加快土壤微生物在后期培养过程的恢复。实验结果为验证土壤有机质矿化的“调节阀”假说提供科学证据，深化对土壤有机碳矿化规律的认知，为土壤温室气体排放和全球变暖过程控制提供理论基础。