亚热带造林树种影响土壤保氮的微生物机制

Nitrogen (N) is one of the most limiting nutrient for plant growth. Enhancing soil N retention capacity can not only increase the primary production of forest ecosystems, but can also decrease environmental pollution caused by N losses. Tree species has been known as an important factor influencing the biogeochemistry cycling of N. Therefore, to identify the mechanism of tree species affecting soil nitrogen retention capacity, it is necessary to understand how tree species influence the population dynamics and function of N cycling-related functional microbes. Our previous studies found that the litter C/N ratio is a deterministic factor affecting the functional gene abundances of N cycling-related microbes. We speculate that tree species characterized by lower litter C/N ratios could facilitate soil N retention capacity through inhibiting soil nitrification mediated by ammonia-oxidizing archaea and denitrification mediated by denitrifiers, while enhance soil N fixation mediated by N-fixing bacteria and dissimilatory nitrate reduction to ammonium mediated by nitrate-ammonifying bacteria. Based on a common garden experimental platform in Sanming field station, Fujian province, this project aims to explore the impacts of subtropical afforestation tree species on the abundance, community structure and diversity of functional microorganisms, as well as gross transformation rates of nitrogen cycling, and therefore to identify the microbial mechanisms of subtropical afforestation tree species influencing soil nitrogen retention. The expected results of this project will provide scientific basis for the selection and evaluation of ecological functions of subtropical afforestation tree species.

氮素（N）是限制植物生长最重要的营养元素之一。通过提高土壤保氮能力，可以增强森林生态系统的初级生产力，减缓氮损失造成的环境污染。树种是影响森林生态系统土壤氮素生物地球化学循环的重要因素。明确树种对氮循环功能微生物种群动态和功能的影响，是揭示树种影响土壤保氮微生物机制的基础。我们前期研究发现，凋落物碳氮比（C/N比）是影响氮循环功能微生物丰度最重要的因子。我们推测：凋落物C/N比低的树种可能通过抑制由氨氧化古菌介导的硝化作用和反硝化细菌介导的反硝化作用，以及促进由固氮菌介导的固氮作用和异化硝酸盐还原菌介导的异化硝酸盐还原为铵过程，从而有利于土壤保氮。本项目依托福建三明野外站同质园实验平台，研究主要造林树种对功能微生物丰度、群落结构和多样性及氮循环总转化速率的影响，揭示亚热带造林树种影响土壤保氮的微生物机制。研究结果有助于为造林树种的选育和生态功能评价提供科学依据。

氮是限制植物生长最重要的大量营养元素之一。增强土壤保氮能力是提高氮素利用效率的前提和关键，有利于提高森林生态系统的初级生产力，并减缓氮损失造成的环境污染。树种是影响森林生态系统土壤氮素生物地球化学循环的重要生物因素。明确树种对氮循环功能微生物种群动态和功能的影响，是揭示树种影响土壤保氮微生物机制的基础。此项目分别以福建南平峡阳林场和三明同质园长期种植的人工林为研究对象，分析树木叶片、细根和凋落物功能性状，结合氮循环功能微生物群落动态及15N同位素示踪模型，阐述不同人工林树种影响土壤氮循环的微生物机制。发现杉木叶片干物质含量、叶片纤维素含量、凋落物C/N比和土壤无机氮含量均显著高于米老排，而米老排叶片比叶面积、凋落物量、凋落物镁含量、土壤总碳和土壤C/NO3-显著高于杉木。树木叶片比叶面积、凋落物磷、氮和镁含量与硝化和反硝化相关的功能基因丰度呈显著正相关，而叶干物质含量和凋落物碳氮比与功能基因丰度呈显著负相关。相比于资源获取型树种，资源保守型树种可以通过降低氨氧化微生物和反硝化细菌丰度，降低土壤硝化和反硝化速率，而提高异化硝酸盐还原菌的丰度，增强硝酸盐异化还原成铵，从而减少土壤中硝酸盐淋溶，增强土壤中以铵态氮作为速效氮的能力，最终提高土壤氮保留能力。该项目研究为开发亚热带人工林种植模式提供有利科学支撑，并服务于我国林业质量提升的重大需求。