我国东北典型森林土壤氮气产生的微生物过程及其贡献

Forest soils are the important nitrogen (N) pool in the terrestrial ecosystems, and play a critical role in regulating regional and global N balances. Nitrogen loss pathways from soils include N leaching and gaseous losses. However, little is known about the gaseous N losses, especially dinitrogen (N2). Under the context of altered global N deposition, the negative effects of N loss can be mitigated if more N is emitted back to the atmosphere in the form of N2. In this proposed project, we will quantify N2 losses from soils in two typical temperate forests in northeastern China and explore their responses to long-term N deposition. The 15N tracer experiments with different labelled substrates (ammonium, nitrate and nitrite) will be conducted and 15N of sampled N2 will be determined by a continuous flow isotope ratio mass spectrometry (IRMS). Using isotope pairing technique we will partition contributions of soil microbial N processes to N2 losses, including denitrification, anaerobic ammonia oxidation and codenitrification, and link them to the environmental factors and abundance of functional genes related to N2 losses. Overall, through the performance of the proposed project, we expect to increase the understanding of gaseous N losses in forest soils and their response to N deposition and of terrestrial N biogeochemical cycling, and also to increase the ability to predict future patterns of forest ecosystem N cycling in response to global changes.

森林土壤是陆地生态系统中重要的氮库，在调节区域及全球氮素平衡中发挥着重要的作用。氮损失途径包括淋溶损失和气态氮损失，然而目前对于气态氮损失，特别是氮气损失量及途径还不清楚。在全球氮沉降格局改变的背景下，如果过多的氮输入以氮气形式返回大气则一定程度上可以减缓氮沉降造成的环境负效应。土壤氮气产生的途径主要有反硝化、厌氧氨氧化和共反硝化三个微生物过程。本项目拟选择我国东北地区天然次生林和落叶松人工林为研究对象，依托氮沉降模拟样地，运用15N示踪技术和微生物分子生物学分析技术，量化森林生态系统土壤氮气释放速率，区分微生物过程对氮气损失的贡献，揭示环境因子和氮循环微生物功能基因与氮气损失的关联，并探索大气氮沉降对森林土壤氮气损失的影响。本项目的实施能够加深我们对森林土壤气态氮损失及其对氮沉降的响应的认识，增强对森林生态系统氮循环及其对全球变化的预测能力，丰富对陆地生态系统生物地球化学循环的理解。

本项目对自然氮沉降状态下的清原次生混交林和落叶松人工林、帽儿山和长白山次生混交林土壤进行氮气排放速率及其于温度敏感性进行了研究，同时探究其对氮沉降响应。所研究的3个站点森林的氮气排放速率范围5.2~39.3 nmol N g soil-1 h-1，森林土壤氮气排放速率和土壤碳氮含量呈显著正相关关系。微生物过程贡献分析表明东北三个站点土壤氮气产生的主要过程均是反硝化作用，比例达到83.9-100%。混交林土壤氮气产生温度敏感性Q10值为2.75~3.72，落叶松人工林土壤氮气Q10值低于混交林，为2.11。氮添加虽然促进了氮气的产生，但降低了氮气产生的温度敏感性。在Soil Biology and Biochemistry刊物发表1篇文章，在应用生态学报发表1篇文章，另外部分数据已经成稿，计划投Soil Biology and Biochemistry刊物。