沙漠化逆转过程土壤碳库演变对环境水热变化的响应机制

Large-scale ecological controlled desertification soil may be the potential carbon sink of sequestering greenhouse gases and mitigating climate change, thus soil carbon pool dynamic characteristics and mechanisms were urgent need to be proven in the repair reversal process. The project was based on the significant different environment water and heat conditions with wind dry season and rain hot season in Northern Shaanxi desert region, and analyze the change of soil total carbon, carbon fractions and carbon respiration on Mu Us sandy Land in the repair reversal process and corresponding conditions, in order to determine the response relations of soil carbon content and carbon flux evolution characteristics to environmental water and heat changes and propose the effect of desertification ecological restoration to improve the soil carbon stock. And further explore the response relationship of soil biochemical properties (microbial quantity, enzymes activity and soil calcium and magnesium ion, bicarbonate radical, alkalinity, cation exchange capacity and electrical conductivity) change characteristics in different hydrothermal conditions to soil carbon pools and carbon flux evolution, establish coupling relationship model of environmental water and heat conditions - soil biochemical properties - soil carbon pool, and reveal the response mechanism of soil carbon pool evolution to environmental water and heat changes. The results were great scientific significance to master sandy ecosystem carbon stock change functions in the global change and the carbon cycle and provide a scientific basis for restoration and reconstruction of desertification ecosystem.

大规模生态治理的沙漠化土壤可能是吸存温室气体和缓解气候变化的潜在碳汇。因此，亟需探明其修复逆转过程中土壤碳库的动态变化特征及机制。本项目基于陕北沙区风旱季、雨热季明显差异的环境水热条件，分析毛乌素沙地沙漠化土壤总碳、碳组分及碳呼吸通量在修复逆转过程及对应水热条件下的变化状况，明确土壤碳库和碳通量的演变特征及对环境水热条件变化的响应关系，提出沙漠化生态修复提升土壤碳库的效应；并进一步探讨不同水热条件影响的土壤生化性质（微生物量、酶活性及土壤钙镁离子、碳酸氢根、碱度、阳离子代换量CEC、电导率EC）变化特征与土壤碳库及碳通量演变的响应关系，建立环境水热条件-土壤生化特性-土壤碳库的耦合关系模型，揭示土壤碳库演变对环境水热条件变化的响应机制。研究结果对掌握沙地生态系统碳库变化在全球变化及碳循环中的作用极具科学意义，可为沙漠化生态系统的修复、重建提供科学依据。

大规模生态治理的沙漠化土壤可能是吸存温室气体和缓解气候变化的潜在碳汇。因此，亟需探明其修复逆转过程中土壤碳库的动态变化特征及机制。本项目基于陕北沙区风旱季、雨热季明显差异的环境水热条件，选择榆林毛乌素治沙林区流沙地、半固定沙地及植被恢复20-50年的乔木和灌木林地，分析土壤总碳、碳组分及碳呼吸通量在沙漠化修复逆转过程及对应水热条件下的演变特征。并进一步探讨了不同水热条件影响下的土壤生化性质变化特征与土壤碳库及碳通量演变的响应关系，以揭示土壤碳库累积效应及其对环境水热条件变化的响应机制。结果表明，沙地植被恢复到55和50年生的灌木和乔木林时0~20 cm土壤总有机碳无机碳分别比流沙地增加7.3和4.6倍，说明固沙林有着显著的固碳效应。并且土壤总有机碳积累量75%来自于砂粒碳和粉粒碳的增加，它们年均增长速率也都显著高于黏粒碳，表明砂砾和粉粒是毛乌素沙地治沙造林土壤固存碳的主要形式。沙漠化逆转植被恢复后土壤碳排放速率显著高于流沙样地，但碳排放量并没有随植被恢复年限延长而显著提高。在灌木林地20年和30年林地土壤呼吸速率平均达到99.4mg CO2/h/m2，且显著高于55的林地；乔木各林龄地土壤呼吸速率无显著差异，平均为60.3 CO2/h/m2。两种林地土壤呼吸速率随温度升高显著增大，但两种植被恢复林地下土壤呼吸速率与土壤水分并无协同变化特征，说明这些沙地土壤碳呼吸对温度响应敏感于土壤温度。冗余分析说明土壤碳库受土壤全磷、全钾、pH等影响较小，但与土壤微生物碳和氮、碱性磷酸酶活性相关性最紧密，说明它们是驱动沙漠化逆转过程土壤碳库变化的最关键环境因素。这些结果对掌握沙地生态系统碳库变化在全球变化及碳循环中的作用极具科学意义，可为沙漠化生态系统的修复、重建提供科学依据。