半干旱沙地退化植被恢复对土壤氮转化的影响机制

In the present day with large global changing, vegetation composition and primary productivity in terrestrial ecosystems strongly affect soil nitrogen input, soil microbe composition and structure, and soil nitrogen cycling. However studies of interrelationship between vegetation composition changes and soil nitrogen cycling in desertified areas closely related to global climate change are still lacking. Therefore, understanding the influencing mechanism of degraded sandy vegetation restoration on soil nitrogen transformation is very important to give the useful reference in theory and application of structure and function restoration of degraded ecosystems in desertified areas. In this project, Horqin Sand Land in the whole desertification converse processes is taken as the research region. Based on the field monitoring and control experiments of artificial simulation, we have used some quantitive methods to carry out a series of overall studies on the soil transformation rate, changes of carbon and nitrogen allocation and its components, and soil microbe composition and structure in the different dominant species, species compositions and different stages of degraded vegetation restoration. These studies will quantitive give the rate and flux of soil nitrogen mineralization, nitrification and denitrification and their key influencing factors, examine their quantitive relationships among plant composition, soil properties, soil microbe composition and structure, and soil transformation, reveal the effects of restoration succession of degraded sand vegetation on soil microbe composition and structure, illustrate the role of soil microbe in processes of soil transformation, and discuss the feedback effect of soil nitrogen accumulation and its availability on plant growth and its biomass allocation. The purpose of this study is to provide some scientific rationales or theory basis and practice support for the further study of ecosystem nitrogen cycling and management of budget balances of carbon and nitrogen in this region.

全球变化背景下陆地生态系统植被组成及生产力的改变影响着土壤氮的输入和土壤微生物组成，进而影响土壤氮循环。与全球变化密切相关的沙漠化地区植被组成和土壤氮循环相互关系的研究相对缺乏。研究退化植被恢复对土壤氮转化的影响机制对于沙漠化地区生态系统结构与功能的恢复具有重要的科学意义。本研究以处于沙漠化整体逆转的科尔沁沙地为研究区域，通过野外观测和模拟控制实验，开展沙地退化植被恢复不同阶段、优势物种和物种组成下的土壤氮转化、植物-土壤碳氮分配及其变化、土壤微生物群落组成与结构特征研究，确定沙地土壤氮矿化、硝化和反硝化速率及其决定因素，建立沙地植物组成、土壤特性、土壤微生物群落结构和土壤氮转化之间的数量关系，阐明沙地植物组成变化对土壤微生物群落结构的影响，明确沙地土壤微生物在土壤氮转化过程的作用，探讨沙地土壤氮积累及可利用性变化对植物的反馈作用，为区域碳氮收支与平衡管理和氮循环的深入研究提供科学依据。

风沙区土地沙漠化或退化土地恢复改变了原有植被组成及生物量，影响着土壤碳氮积累及其转化过程，进而影响生态系统的结构和功能。本研究通过连续5年的定位监测实验，对科尔沁沙地退化植被恢复过程中不同阶段土壤氮转化速率、动态变化规律及其影响因素进行了系统的研究。结果表明：1）沙地退化植被恢复演替改变了植被-土壤系统中碳氮化学计量特征，而5年封育导致了不同恢复阶段植物优势度改变，增加了地上植物和土壤氮含量；2）沙地退化植被恢复过程中植被-土壤系统碳氮储量逐渐增加，5年封育导致半固定沙丘植被和固定沙丘土壤氮储量增加；3）沙地退化植被恢复过程中土壤铵态氮含量逐渐降低、硝态氮和无机氮含量逐渐增加，土壤硝态氮在无机氮库中占有较大比例；土壤硝态氮、铵态氮和无机氮含量存在明显的年际和季节分异规律，生长季前期较高、8月份较低，2015年土壤硝态氮和无机氮含量较高；4）沙地退化植被恢复促进了土壤氮硝化和矿化过程，2015年土壤氮的净硝化和净矿化速率较高；土壤净硝化速率的季节差异不显著，而土壤净氮矿化速率8月份相对较高；5）沙地植被、土壤和气候因子共同决定着土壤氮转化速率，土壤特性对5-8月份土壤氮转化速率贡献较大，而降雨和空气温度对8月份土壤氮转化速率影响较大；6）沙地植物为了适应风沙环境而形成了独特的功能性状，影响着土壤细菌多样性和群落的氮素利用效率；而不同阶段的优势物种通过改变土壤水分和养分，过滤了土壤真菌群落组成，降低了土壤真菌多样性；7）生长季减少的土壤无机氮含量，特别是有机氮转化后形成的硝态氮含量影响着沙地植被的生长及其发育特征。本研究阐明了沙地退化植被恢复过程中土壤无机氮含量的变化及转化规律，确定了沙地生长季及年际间土壤氮转化速率及其关键影响因素，明确了沙地退化植被恢复对土壤氮转化及可利用性的影响及其反馈关系，揭示了沙地退化植被恢复对土壤氮转化的影响机制，为半干旱沙区退化生态系统的恢复和管理提供科学依据。