喀斯特草地土壤氮营养关键微生物群落对外源氮的响应

Mitigating the N stress on Karst grassland is of great significance for accelerating the process of degraded vegetation restoration and improving the ecological service of artificial pasture. The key scientific issue in this study is how coupling relationships between soil N transformation processes and the arbuscular mycorrhizal fungi（AMF） and the key functional microbial communities of N cycling to exogenous N inputs in grasslands from Karst regions. Based on nitrogen deposition simulation and nitrogen fixation plant long-term experiments, using typical karst natural grassland (natural recovery after reclamation) and artificial grassland (Guimu 1 pasture) as study object, field monitoring and indoor analysis methods, and 15N isotope tracer and high-throughput sequencing techniques, The project intends to 1) determine the Effects of the key microbial communities (AMF, ammonia-oxidizing bacteria and archaea, nitrogen-fixing bacteria and denitrifying bacteria) and soil microflora to exogenous N in these two types of karst grassland ecosystems; 2) elucidate the effects of the key processes of nitrogen cycling (nitrogen mineralization, nitrogen fixation, nitrification and denitrification) and these fluxes to exogenous N; 3) analyze the relationship between soil AMF and the microorganisms in the key processes of the nitrogen cycling; 4) reveal the responses and its mechanisms on key functional microbes and their driving processes for soil N nutrients to exogenous nitrogen in karst grassland ecosystem, combined with the soil physicochemical properties and the results of above-ground vegetation communities. The results should provide the scientific foundation for promoting the restoration of degraded vegetation and sustainable management of artificial pasture in Karst regions.

缓解喀斯特草地N素胁迫对于加速退化植被恢复进程和提升人工牧草地生态服务具有重要意义。项目拟围绕喀斯特草地土壤N转化过程与关键功能微生物群落的耦合关系及其如何响应外源N输入这一关键科学问题，以典型喀斯特撂荒后自然恢复草地和桂牧1号人工草地为研究对象，基于氮沉降模拟和固氮植物引种长期试验的野外监测和室内分析，利用15N同位素示踪和高通量测序等技术，明确外源N对两类喀斯特草地生态系统土壤丛植真菌（AMF）、氨氧化细菌和古细菌、固氮菌与反硝化细菌群落和土壤微生物区系的影响，阐明外源N对土壤氮素氮矿化、固氮、硝化和反硝化及其通量的作用，解析土壤AMF与氮循环关键过程微生物之间的关系，结合土壤理化性质和地上植被群落调查与测定结果，揭示喀斯特草地土壤N营养关键功能微生物及其驱动过程与功能对外源氮的响应及其机制，为促进喀斯特自然草地植被恢复和人工草地可持续管理提供科学依据。

外源氮输入（豆科固氮灌木、氮沉降和氮肥）可以增加土壤氮的供应和缓解氮限制，对加速退化植被恢复进程和提升人工牧草地生态服务具有重要意义。土壤微生物是介导养分转化的关键成员，土壤丛枝菌根真菌（AMF）和氮转化关键微生物是改善土壤质量和氮素营养的重要功能微生物。本文以自然草地和人工牧草地为研究对象，研究喀斯特草地土壤N营养关键功能微生物及其驱动过程与功能对外源氮的响应及其机制。.研究结果发现季节变化显著影响AMF和固氮菌，外源氮输入对AMF和固氮群落的影响主要在生长季，通过调控AMF和固氮菌来提高不同氮输入方式的有效性需要考虑季节因素。喀斯特自然草地中，氮添加可能会加剧土壤磷的不足，草丛群落通过提高AMF多样性提高磷的吸收; 磷添加通过提高固氮菌的多样性有利于生物固氮。深紫木蓝固氮能力高于紫穗槐，但高密度种植深紫木蓝降低AMF和固氮菌丰度，表明低密度种植深紫木蓝是喀斯特自然草地缓解氮限制的有效途径。人工牧草地中，AMF和固氮菌群落间的竞争在氮肥处理高于紫穗槐，豆科灌木相比氮肥能有效提高AMF和固氮菌多样性，有效改善土壤氮输入。.喀斯特地区人工牧草地，氮肥添加和豆科灌木均显著增加土壤N2O累积排放量，氮肥施用更容易促进土壤气态氮的损失。土壤硝化和反硝化关键微生物类群受季节和外源氮的影响。高有效氮浓度条件下促进氨氧化细菌(AOB)的生长，相比于氮肥添加，固氮植物种植可降低土壤氨氧化古菌(AOA)和AOB丰度，从而减弱喀斯特地区人工牧草地土壤硝化过程，是减少硝化过程产生N2O的重要措施。外源氮输入使土壤反硝化细菌nirK基因丰度也有增加的趋势，高氮输入同样抑制了反硝化细菌nirK基因丰度，但外源氮输入并未显著改变反硝化细菌nosZ基因丰度。土壤AOA和nirK是喀斯特地区人工牧草地土壤N2O排放的主要微生物因子，nirK基因丰度对N2O排放通量具有显著的正向作用；而AOA对N2O排放通量具有显著的负向作用。.上述研究不仅加深理解喀斯特草地外源氮输入对关键微生物类群的影响，而且为喀斯特草地提供有效管理措施。