岩溶区钙对土壤有机碳稳定性的影响机制研究

Soil carbon pools play an important role in the global carbon cycle. The stability of soil organic carbon affects the absorption/release CO2 directly, which subsequently impacts the global carbon cycle. Many researchers have demonstrated that soil calcium could enhance the stability of soil organic carbon. However, the mechanism has not yet understood. The calcium-rich and slightly alkaline limestone soil in karst area is the most suitable samples for mechanism research of soil calcium effecting on organic carbon stability. The limestone soil of different succession stages and the similar type of limestone soil from different depth at Guilin Mao Village Karst Ecological Experimental Site will be collected to reveal: 1) the physical protection mechanism of different calcium levels on soil organic carbon; 2) the chemical accumulation and combination mechanism of soil organic carbon in different calcium content soil; 3) the influence of calcium on soil organic carbon’s decomposition, transformation, and sequestration. Of course, the research methods for each aspects are different but advanced, e.g. a combination of technologies such as scanning electron microscopy, supporting X- ray spectrometer (EDX), and synchrotron radiation computed tomography (CT) techniques would be used in the first section; solid 13C nuclear magnetic resonance (13CNMR) technology would be applied in the second part; while the laboratory incubation experiments will be conducted in the last aspects. This research results will provide scientific basis for soil carbon sequestration potential and its maintain mechanism in karst area. Meanwhile, this research can also offer the theoretical support for mechanism research of karst soil response to global change.

土壤碳库在全球碳循环中占有重要的地位，土壤有机碳的稳定程度直接影响到土壤吸收/释放CO2的能力，进而影响全球碳循环过程。已有研究表明，土壤钙可以增加土壤有机碳的稳定性，而其影响机理目前尚不清楚。岩溶区土壤具有富钙偏碱的特点，是研究土壤钙对有机碳稳定性影响机制的理想场所。本项目以桂林毛村岩溶生态试验场不同演替阶段的石灰土以及同种石灰土不同土层深度土壤为研究对象，利用扫描电镜与辅助的X射线能谱仪及同步辐射显微CT技术对不同钙含量土壤及团聚体表面结构和内部微结构进行扫描，探明不同钙水平对土壤有机碳的物理保护机制；利用固体13C核磁共振技术等技术，阐明不同钙含量土壤中有机碳积累的化学稳定与结合机制；利用室内培养试验，通过设置不同浓度梯度钙含量，揭示钙对土壤有机碳分解、转化、固持的影响。上述研究成果将为岩溶区土壤碳固持潜力及其维持机制研究提供科学依据，为岩溶区土壤对全球变化响应机制研究提供理论支撑。

土壤钙对有机碳稳定性具有重要作用，岩溶区土壤具有富钙偏碱的特点，是研究土壤钙对有机碳稳定性影响机制的理想场所。本项目以桂林毛村岩溶生态试验场不同演替阶段的石灰土（即红色石灰土、棕色石灰土和深棕色石灰土）为研究对象，将土壤钙形态按照Tisser方法将土壤钙形态分为5种，水溶态钙、交换态钙、酸溶态钙、有机结合态钙和残渣态钙。分别研究了不同钙形态与土壤水稳性团聚体、土壤有机碳化学结合形态及化学结构和有机碳矿化等之间的关系，结果显示：（1）除有机结合态钙与各粒径团聚体之间的相关关系均不显著；其它各形态钙与各粒径团聚体之间均存在正的或负的相关关系。这说明各形态钙对土壤团聚体组成均具有重要的影响，在土壤团聚体对有机碳的物理保护中具有重要的作用，但是各形态的作用不相一致。（2）三种土壤中铁铝键结合态有机碳平均值为钙键结合态有机碳的14倍。钙键结合态有机碳仅与有机结合态钙呈显著正相关关系；铁铝键结合态有机碳与酸溶态钙和有机结合态钙分别均呈显著正相关关系。红色石灰土以烷基碳和烷氧碳占多数，而深棕色石灰土中则以芳香碳占优势。水溶态钙与烷基C、烷基C/烷氧C比值均呈显著正相关关系；酸溶态钙与疏水C/亲水C比值呈显著负相关关系；残渣态钙与烷基C、烷基C/烷氧C比值均呈极显著负相关关系，而与烷氧C呈显著负相关关系。（3）土壤有机碳矿化所释放的CO2-C的分配比例与水溶态Ca和残渣态Ca分别呈极显著负相关和正相关关系；培养90天累积矿化量与有机结合态Ca呈显著正相关关系。培养前后，纤维素酶活性增加幅度较大，表明纤维素酶是参与岩溶区土壤有机碳分解的重要酶类。纤维素酶活性在培养前与残渣态钙呈极显著正相关关系，而与水溶态钙呈极显著负相关关系；在培养后与残渣态钙呈极显著负相关关系。上述研究成果可为岩溶区土壤碳固持潜力及其维持机制研究提供科学依据，为岩溶区土壤对全球变化响应机制研究提供理论支撑。