古尔班通古特沙漠不同类型生物土壤结皮氮素组成差异和转化特征

Nitrogen (N) is a key factor which limits productivity of desert ecosystem. N fixation of biological soil crusts (BSCs) could supply abundant nutrients for the whole ecosystem. The fixed N by BSCs could be transformed to different N forms, and thus influence plant growth and community succession. However, the N composition and many processes of N transformation in BSCs are not clear. Three BSCs, including algae crusts, lichen crusts and moss crusts, widely distribute in Gurbantunggut Desert. In order to investigate the N distribution in BSCs, three types of BSCs with bare sand soil will be selected as controls to measure total N, nitrate, ammonium and organic N content. Using isotope and molecular technology, we will also analyze the N fixation efficiency, microbial biomass N, net N mineralization rates, nitrification rates, denitrification rates, abundance of N transformation and richness of related genes. All the above information will be helpful to reveal details of N immobilization and transformation processes. The climate and soil data collected in different seasons will then be combined to illustrate the key environmental factors that affect N cyclic processes in BSCs. Then, the model of spatial N distribution and dynamics can be constructed in small scale. The study of N distribution, N immobilization ability and N transformation differences among different BSCs is beneficial for us to the understanding of the complex N cycle in arid land and driving factors of biological activity related to N in BSCs. This work is believed to provide enough data for the evaluation of ecological effects of BSCs and the law of vegetation succession.

氮素是荒漠生态系统生产力的重要限制因子，生物土壤结皮能够固定大气中的氮素，是该生态系统重要的氮素来源。结皮所固定的氮素转化为不同形态的氮，进而影响植物生长及群落演替。然而，目前对结皮氮素组成及其转化许多过程的了解尚不充分。本项目拟以古尔班通古特沙漠镶嵌分布的藻类、地衣和苔藓结皮为对象(裸沙为对照)，揭示不同类型结皮中主要形态氮素(如全氮、硝态氮、铵态氮和有机氮等)的组成特点；将同位素和分子生物学等技术相结合，通过测定与氮素转化密切相关的指标(如固氮速率、微生物量氮、矿化速率、硝化反硝化速率和氮转化功能基因多度等)对比分析不同类型结皮氮固持及转化过程的差异；结合不同季节的气候和土壤环境因子探讨影响结皮氮素转化的关键因素，构建小尺度氮素空间分布及动态模式。该研究有助于阐明干旱区氮素循环的精细过程以及与结皮中氮素相关各生物过程的驱动因子，为全面评估结皮的生态效应和植物演替方向提供数据支持。

氮素是荒漠生态系统生产力的重要限制因子，生物土壤结皮能够固定大气中的氮素，是该生态系统重要的氮素来源。结皮所固定的氮素转化为不同形态的氮，进而影响植物生长及群落演替。然而，目前对结皮氮素组成及其转化许多过程的了解尚不充分。本项目在古尔班通古特沙漠设置样地，研究不同结皮类型各形态氮素的动态，同时结合北美主要荒漠系统结皮的氮素固定和转化情况，综合分析不同季节效应，重点探讨水热变化对氮素形态和转化能力的影响。主要发现：1）揭示了不同结皮类型不同形态氮素的动态变化规律，为荒漠系统植物多样性维持的营养基础提供参考。2）发现不同结皮氮素输入与转化随温度而变化，其平衡被打破，预计温度增加将有更多的氮素流失。3）确定植物群落中各有机体对氮素的敏感性从大到小依次为苔藓结皮>藻类结皮>地衣结皮， 0.5 g N m-2a-1的氮沉降将影响荒漠生态系统稳定。4）从季节和年际动态揭示持续的氮素增加导致植物群落改变的级联效应特点，并导致植物群落结构和功能发生退化。该研究有助于阐明干旱区氮素循环的精细过程以及与结皮中氮素相关各生物过程的驱动因子，为全面评估结皮的生态效应和植物演替方向提供数据支持。本项目共发表文章7篇，其中SCI刊物5篇，CSCD刊物2篇。第一标注的SCI论文3篇，第2标注SCI论文1篇，全部为JCR分区一区刊物。项目的部分研究成果获得新疆维吾尔自治区科学技术进步一等奖（自然科学类），负责人排放第二。