中国典型生态系统大气氮沉降和磷沉降：格局、控制因素及其对生产力的影响

China has been considered as one of three regions with higher atmospheric nitrogen (N) deposition, and it was predicted that the intensity of atmospheric N deposition will further increase with the development of agriculture and industry in future as a result of rapid increase in the anthropogenic emission of reactive N, through burning fossil fuels and fertilizer application. On the one hand, atmospheric N deposition has a positive effect on maintaining plant productivity of terrestrial ecosystems through enhancing the N availability; on the other hand, excessive N deposition has negative impacts on ecosystem health and services, such as N saturation, soil acidification, and loss of biodiversity. Therefore, it is important to understand the spatio-temporal patterns and influencing factors of N deposition to evaluate its ecological effects on terrestrial ecosystems, and to provide a scientific basis for global change research..　　It is necessary to consider atmospheric N and phosphorus (P) deposition together in order to scientifically evaluate the increasing atmospheric deposition under global change scenarios,　because N and P both play important roles in different component in terrestrial ecosystems and are commonly coupled. In this program, we will monitor the monthly atmospheric N and P deposition in rainfall at 40 stations from the Chinese Ecosystem Research Network through measuring total N (TN), total dissolved N (TDN), ammonium (NH4+–N), nitrate (NO3––N), dissolved P, and total P. Furthermore, we will produce the data of atmospheric N deposition from 1980s~2010s and the data of P deposition in 2010s in Chinese terrestrial ecosystems combining our monitoring data and publicly published data. On basis of multi-source data, we would explore the influence of atmospheric N and P deposition on Chinese terrestrial ecosystems from the view of community structure, productivity, and biodiversity. .　　Here, we will address the following scientific issues: 1) what are the long-term dynamics of atmospheric N deposition in Chinese terrestrial ecosystems and the mainly influencing factors; 2) what is the quantity and spatial pattern of atmospheric P deposition; 3) how atmospheric N and P deposition influences the structure and functions of terrestrial ecosystem in view of the quantity of deposition, the composition of atmospheric N deposition, and N:P stoichiometry.

大气氮沉降已成为陆地生态系统可利用性氮的重要输入途径，如何科学地评估其生态效应受到科学家高度关注。科学家已对我国大气氮沉降开展了较多工作，但大气磷沉降的研究却鲜有报道；鉴于氮和磷在生态系统不同组织层次中的重要性及其耦合关系，未来应将二者有机结合。本项目将基于前期在中国典型陆地生态系统建立的大气氮沉降联网观测平台（约40个生态站），进一步开展大气氮沉降观测，同时创新性地开展中国区域大气磷沉降观测，再结合公开发表数据、野外控制实验meta-分析结果和长期监测的生产力和pH值等数据，综合评价日益增加的大气沉降（氮磷输入）对中国区域陆地生态系统生产力的影响。重点关注的科学问题如下：1）中国区域氮沉降的长时间尺度的时空动态及其主控制因素；2）磷沉降的空间格局和主控因素；3）从大气氮磷沉降量、化学计量特征（N:P）、氮沉降组分（NH4＋:NO3－）等角度探讨大气氮和磷沉降对陆地生态系统生产力的影响。

基于中国湿沉降监测网络（China_WD）开展了大气（雨水）氮磷沉降的联网监测，获取了连续四年的大气雨水化学性质及氮磷沉降数据，结合文献数据，建立了中国区域陆地生态系统大气湿沉降组分变化和空间格局数据库。在此基础上，分析了氮湿沉降组分、空间格局及其影响因素，阐明了过去三十年中国氮沉降的动态变化、主要影响因子及变化趋势；初步评估了大气氮沉降的生态环境效应，评估了氮沉降对生态系统酸化的影响、对森林生态系统固碳的贡献；首次基于联网观测评估了全国尺度的磷沉降速率，发现大气湿沉降中较高的氮磷比，推测大气沉降导致的氮磷输入的不平衡可能会强化生态系统的磷限制。相关成果可以为深入评估氮沉降的生态环境效应提供数据支撑和理论基础。项目资助发表学术论文13篇，其中第一标注SCI论文5篇，第二标注SCI论文4篇，超额完成预期目标。