农牧交错带半干旱草地生态系统碳-氮耦合关键过程的养分调控机理

Carbon (C) and nitrogen (N) coupling is dependent on the utilization and degradation of soil microbe to soil organic substance. In order to understand the C-N coupling relationship of semi-arid grassland, investigating the role of soil microbial in carbon-nitrogen cycle has highly concerned by ecologists. And how the soil microbial responds to the changes of C-N cycle caused by nutrient addition is still not clear. This project is based on the multi-nutrient networking experiment platform that has been established in the agro-pastoral ecotone in northern China. The purpose of this study is to determine the responses of C-N coupling (including productivity, diversity, soil respiration, ecosystem gas exchange, soil mineralization and nitrification, etc.) to multi-nutrient additions. Using me thods of 15N and 13C isotope tracing, phospholipid fatty acid method and high-throughput sequencing, combining laboratory incubation experiments, the study will be quantitatively analyze the variations of soil microbial community richness and diversity in response to multi-nutrient additions. The effects of microbe on dextran depolymerization and glucose consumption, protein depolymerization and amino acid consumption, nitrogen mineralization and ammonium consumption, nitrification and nitrate depletion will be researched for exploring the regulatory mechanism of soil microbe to ecosystem C-N coupling. This study will provide more data and theoretical support for predicting the impact of multi-nutrient on the C-N cycle in ecologically fragile regions of China.

生态系统碳、氮循环耦合关系通过土壤微生物降解和利用有机质而紧密相连，研究土壤微生物在碳、氮循环过程中的作用是理解半干旱草地生态系统碳-氮耦合循环的关键。土壤微生物如何响应养分输入引起的碳-氮耦合循环过程变化，受到生态学者的高度关注。本项目拟依托北方农牧交错带半干旱草地生态系统已建立的养分添加联网试验平台，探讨添加氮、磷、钾对碳-氮耦合过程（生产力、多样性、生态系统气体交换、土壤呼吸、土壤氮矿化/硝化等）的影响；并结合室内培养实验，采用15N和13C同位素示踪、磷脂脂肪酸法和高通量测序技术，定量分析养分添加对土壤微生物群落丰富度和多样性的影响；探索添加养分后土壤微生物对葡聚糖和葡萄糖、蛋白质和氨基酸、氮矿化和铵盐、硝化和硝酸盐等物质转化的效率，揭示微生物驱动碳-氮耦合循环过程的养分调控机理，为准确预测由未来气候变化引发的养分改变对生态脆弱区草地生态系统碳-氮循环的影响提供数据支持和科学依据。

厘清植物、土壤微生物如何响应养分输入引起的碳-氮耦合循环过程变化是理解半干旱草地生态系统碳-氮耦合循环的关键。本项目依托北方农牧交错带半干旱草地生态系统已建立的养分添加联网试验平台，对添加氮、磷、钾后碳-氮耦合过程关键环节如生产力、多样性、凋落物分解、微生物群落结构、微生物呼吸与碳限制进行了研究，取得的主要结果如下：（1）氮磷共同添加可增加群落优势度，提高地上生物量，但会降低植物根冠比，对群落植物物种多样性、丰富度无显著影响；（2）氮添加促进了凋落物全碳的降解，但对全氮具有显著抑制作用，对纤维素、木质素降解无显著影响，土壤中硝态氮含量越高凋落物损失速率越低；（3）氮、磷交互显著提高了土壤细菌、革兰氏阳性菌、革兰氏阴性菌和菌根真菌PLFA量，氮氮、磷、钾多养分交互对土壤微生物群落特征无显著影响，养分添加通过改变土壤全氮含量及土壤酸碱度影响土壤细菌PLFA量；（4）碳、氮共同添加可显著提高土壤呼吸速率，高碳处理提高了土壤微生物活性，显著增强了呼吸强度，表明氮添加后草地土壤呼吸速率受到碳源的限制。以上结论对于提升学界对于养分输入与碳、氮循环关键环节互馈关系的认识具有重要科学意义。