封育对宁夏荒漠草原土壤有机碳库及其稳定性的影响

With the implementing of national projects returning farmland to pasture, Ningxia took the policy of enclosure against grazing into full operation from 2003. The ecological environment of some pastures returning better. However, what changes will be occurred of soil organic carbon and its stability? How these changes influence on the regional climate change, carbon cycle and ecosystem stability? These were all problems which should be solved urgently for ecological protection. In this study, we will select the desert steppes which were enclosed against grazing in different years and study the concentration and distribution in different soil depth and different soil aggregate of soil organic carbon and its components, soil structure and its relation with physical protection for organic carbon, differentiation, source and transformation of soil organic carbon, decomposition of soil organic carbon and its temperature sensitivity. On the basis of the investigated results, we will explore the change of soil organic carbon pool and its stability, and seek for the influence mechanism of enclosure on stability of soil organic carbon. All these are aimed at providing theory guidance for increasing carbon sink and reducing emission of grassland ecosystem, which has practical significance for ecological environment construction.

随着国家退牧还草工程项目的实施，宁夏于2003年全面实施了草地围封禁牧，草地生态恢复效果显著。退化草地封育后，土壤有机碳库及其稳定性会产生怎样的变化，这种变化对区域气候变化、碳循环及生态系统稳定性的影响如何，是目前生态保护亟需探讨的问题。 本项目拟以宁夏荒漠草原自然恢复的围封草地为对象，以土壤有机碳稳定性为核心，系统研究退化草地不同恢复阶段土壤有机碳及其组分含量在土壤剖面及不同粒径团聚体中的分布、土壤结构与有机碳物理保护作用的关系、土壤有机碳分异及其来源和转化、土壤有机碳分解及温度敏感性等；探讨封育草地不同恢复阶段土壤有机碳库及其稳定性变化，阐明封育措施对荒漠草原土壤有机碳的稳定性影响机制。旨在为草地生态系统碳增汇/减排技术和生态系统管理提供理论指导，对宁夏生态环境建设具有重要意义。

以宁夏荒漠草原自然恢复的封育草地为对象，研究了不同恢复阶段草地土壤有机碳及其组分含量在土壤剖面及不同粒径团聚体中的分布、土壤结构与有机碳物理保护作用的关系、土壤有机碳分异及分解、转化等；探讨了封育措施对荒漠草原土壤有机碳稳定性影响机制。结果表明：荒漠草原0-40cm各土层团聚体稳定性较高和总有机碳含量以封育7年、10年的荒漠草原较高；各粒级团聚体对有机碳的贡献率在0-20 cm浅层以<0.25mm微团聚体较高，20-40cm土层以>5 mm较高。封育7年的荒漠草原可溶性有机碳和易氧化有机碳含量较高。综合土壤团聚体及有机碳稳定性，封育7年是退化荒漠草原自然恢复演替过程中的一个转折。不同封育年限荒漠草原8-10月份土壤呼吸速率7:00-16:00的日变化均成明显的上升趋势；5-10月各封育年限草地土壤呼吸速率呈现先上升后下降的趋势，8-9月份较高，且各封育年限草地显著高于未封育草地。水热复合模型较水分和温度单因子模型更好的解释了土壤呼吸的变化。不同培养温度条件下，各封育年限荒漠草原土壤有机碳矿化均可分为活跃期(0-13d)和惰性期(14-76d)；土壤有机碳累积矿化量随温度的增加总体呈波动性变化，以25℃培养条件下较高；各封育年限荒漠草原之间土壤有机碳矿化速率及累积矿化量在15℃、25℃培养条件下差异不显著，在5℃、35℃培养条件下以封育9年的草地较高。土壤含水量为25%SSM 和100%SSM时，各封育年限草地土壤有机碳累积矿化量分别以封育12年的草地和未封育草地较高。枯落物添加对各封育年限草地土壤有机碳矿化产生了正激发效应，以封育9年草地的激发效应最强。RDA排序结果表明枯落物有机碳和全氮对土壤有机碳矿化有显著影响，累积解释量为70.87%。各封育年限荒漠草原植物地上部、牛枝子和短花针茅枯落物稳定性同位素δ13C值总体随封育年限的延长偏向正值；封育9年的草地土壤有机碳δ13C值总体更加偏负；不同封育年限草地同一粒级团聚体有机碳δ13C值随土层的加深逐渐趋于正值，0-10 cm表层土壤0.25-2 mm粒级团聚体δ13C值较其他粒径偏负。