黄土高原刺槐林恢复对根际异化硝酸盐还原过程的影响及其机制

Soil mineral nitrogen availability is a key factor affecting the stability of vegetation community and plant root systems in fragile ecosystems. Dissimilatory nitrate reduction is a primary microbiological processes associated with retention and loss of mineral nitrogen in soil systems. Hence, aiming at the ecological function stability and sustainable development of Robinia pseudoacacia L. in the Loess Plateau, the project will be executed in the rhizosphere soil under Robinia pseudoacacia L. plantations of different ages. Based on the stable isotope probing, high throughput quantitative PCR, Illumina MiSeq sequencing and Geochip technologies, the potential rates of dissimilatory nitrate reduction and their relative contribution to the retention and loss of mineral nitrogen in Robinia pseudoacacia L. rhizosphere will be quantified. The active expression, temporal dynamics and interaction of active microbial communities associated with dissimilatory nitrate reduction in the rhizosphere microbitat will be clarified. The ecologial correlations between dissimilatory nitrate reduction processes rates and active function gene groups in the rhizosphere microbitat will be revealed. Overall, this work will provide novel insights into the relative contribution of dissimilatory nitrate reduction to the retention and loss of mineral nitrogen and their ecological associations with active microbial communities in Robinia pseudoacacia L. rhizosphere. This study will provide scientific evidences for enhancing the function and provisioning of Robinia pseudoacacia L. plantations in the Loess Plateau and integrated nitrogen nutrient management.

土壤矿质氮有效性是影响脆弱生态系统地上植被群落和地下根系功能稳定的关键因子，而异化硝酸盐还原过程直接影响土壤矿质氮的蓄持与流失。为此，本项目针对黄土高原广泛分布的刺槐林植被的生态功能稳定性与可持续发展，以不同林龄刺槐根际土壤为研究对象，采用15N稳定同位素示踪、高通量荧光定量PCR、Illumina MiSeq测序和基因芯片等技术，量化异化硝酸盐还原过程速率及其对矿质氮蓄持与流失的影响，探明异化硝酸盐还原功能微生物的活性表达量、演变特征及互作关系，解析异化硝酸盐还原过程速率与活性功能基因群之间的生态关联。旨在明确黄土高原刺槐根际异化硝酸盐还原过程对土壤矿质氮蓄持与流失的相对贡献及其与功能微生物的关联机制，为提升黄土高原刺槐林植被生态服务功能以及制定合理的氮素养分平衡管理策略提供科学依据。

土壤矿质氮有效性是影响脆弱生态系统地上植被群落和地下根系功能稳定的关键因子，而异化硝酸盐还原过程直接影响土壤矿质氮的蓄持与流失。为此，本论文从黄土丘陵区不同恢复年限刺槐根区土壤为研究对象，综合稳定同位素和分子生物学技术，研究了退耕地土壤异化硝酸盐还原过程速率、异化硝酸盐还原微生物群落演变特征及关键环境驱动因子、功能基因的表达量及活性表达量，解析了异化硝酸盐还原过程速率与活性功能基因群之间的定量偶联关系。主要结论如下：1）随刺槐恢复年限的增加，异化硝酸盐还原产铵（DNRA）速率逐渐减小；与农田土壤相比，反硝化速率在恢复35年后显著增加，表明刺槐恢复抑制了DNRA过程，促进了反硝化过程。2）随刺槐恢复年限的增加，DNRA过程的功能基因nrfA的表达量逐渐减小，微生物群落的丰富度和多样性显著降低，从而导致DNRA速率减小。微生物群落中的物种主要为Proteobacteria、Sorangium，有机碳和微生物量碳是影响DNRA微生物群落的关键环境因子；反硝化过程的功能基因napA、narG、nirK、nirS、nosZ的活性表达量在刺槐恢复后期显著增加，微生物群落的丰富度显著增加，从而导致反硝化速率显著增加。微生物群落中的物种主要为Proteobacteria、Azospirillum和Pseudogulbenkiania，有机碳、全磷、有效磷和铵态氮是影响微生物群落的关键环境因子。3）综合分析发现：1）DNRA速率与全磷显著正相关，与有机碳、微生物量碳负相关；反硝化速率与有机碳、微生物量碳显著正相关；2）DNRA速率与nrfA基因的表达量和活性表达量、微生物群落的丰富度和多样性指数存在多种偶联机制，DNRA速率因而受制于菌群多样性和功能基因的联合作用；3）基因活性表达量比值nosZ/(nirK+nirS)是预测反硝化速率的关键变量，反硝化速率受限于菌群丰度和nirK、nirS、nosZ功能基因的联合作用。研究结果可为提升黄土高原刺槐林植被生态服务功能以及制定合理的氮素养分平衡管理策略提供科学依据。

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