风沙区人工植被演变对土壤碳氮截存的影响及潜力研究

The establishment of sand-binding vegetation is the key process to prevent the damage of wind erosion and promote degraded land restoration. There are more than 6 million hm2 of artificial sand-binding vegetation in the sand drift area of China, which are the important ecological shelter in north China, and they effectively improved the habitats in desert area, promoted regional ecological restoration. However, little is known about the impacts of vegetation succession processes on soil habitats, in particular, we know little about the effects of vegetation change on the variations of soil carbon and nitrogen sequestration and potential, these issues are the important prerequisites to elucidate the ecological mechanisms of the restoration and rehabilitation of degraded lands through artificial sand-binding vegetation establishment. Based on the long-term monitoring of the long time-series of artificial revegetation sites, and comparing with mobile sand dunes and natural vegetation area, this project is aimed to elucidate the soil carbon and nitrogen sequestration processes and rates, holding states, sequestration potential and spatial-temporal pattern. Further, quantitatively analyzing the contribution of changes in species composition, structure and functional group to soil carbon and nitrogen storage, quantifying soil carbon and nitrogen sequestration potential of artificial sand-binding vegetation through the analysis of state function of carbon and nitrogen storage and the sequestration rates. The ultimate goal of the project is to provide the basis for comprehensively analyzing the ecological mechanisms of ecological restoration promoted by artificial vegetation.

人工植被建设是遏制风沙危害、促进退化土地恢复的重要途径。我国沙区已有超过600万hm2的人工固沙植被，它们构成了北方重要的生态屏障，有效地改善了沙区生境，促进了区域生态恢复。然而，固沙植被演变过程对土壤生境的反馈影响，尤其是对土壤碳氮储量的改变及潜力，我们知之甚少，这一问题的研究是诠释风沙区通过人工植被促进生态恢复与重建机理的重要前提。本项目利用长时间序列人工植被样地，在长期定位监测的基础上，以相邻地区流动沙丘和天然植被为对照，研究不同演替阶段植被对土壤碳氮截获过程与速率、固持状态、固存潜力及时空格局特征的影响；量化植被组成、结构和功能群改变对土壤碳氮库储量的影响及其机理，通过土壤碳氮储量状态函数、碳氮固存速率的研究预测人工固沙植被区土壤碳氮截存潜力，为全面解析沙区人为促进植被恢复的生态学机理提供依据。

植被恢复重建是促进物种拓殖与定居及土壤系统修复的有效途径之一，更是增加土壤碳氮截存的关键措施。作为陆地生态系统的重要组成部分，干旱沙地生态系统的碳氮固存功能长期被忽视，特别是关于土壤统碳氮储量对该区植被恢复重建的响应仍然存在很大的不确定性，对植被恢复重建后土壤碳氮库动态变化规律、时空格局、截存的动力学特征与潜力认识不足。针对这一现状，本项目利用时间序列人工固沙植被长期监测样地，以相邻地区流动沙丘和天然植被为对照，研究了固沙植被建立后土壤碳氮密度、储量、碳氮库分布特征以及碳氮循环关键过程。结果表明：固沙植被建立后，土壤碳氮密度及储量显著增大，碳氮库变化主要在表层0-10cm。根据模型预测，腾格里沙漠东南缘土壤碳氮库分别需要139和177年恢复到天然植被区水平。植被恢复过程中，土壤中轻组有机碳、颗粒有机碳等物理组分及可溶性有机碳、微生物量碳、酸水解碳等化学组分含量均随着恢复年限的延长而增加，而各组分占比则逐渐减小。有机碳矿化过程受植被恢复年限和水热等环境因子的共同调控作用，土壤潜在可矿化碳比例随植被恢复年限延长而逐渐减小。随植被恢复年限的延长，土壤碳分解酶活性显著增强，水解酶增加的速率大于氧化酶。过氧化物酶和多酚氧化酶是影响土壤有机碳矿化的主要因素，可解释土壤碳矿化量变异的77.2 %。植被恢复使土壤无机氮库储量及净硝化和矿化速率显著增大，显著促进了土壤氮素有效性的增加和氮素循环过程。本研究证实了采用耐旱灌木造林使降水小于200mm的沙区土壤碳氮储量和土壤质量显著提高，促进了碳氮关键循环过程，是区域生态环境改善的有效途径之一。