Ecosystem Dynamics and Global Ecology Laboratory, School of Forestry and Wildlife Sciences, Auburn University, Auburn, Alabama 36849, USA.
Ecol Appl. 2012 Jan;22(1):53-75. doi: 10.1890/10-1685.1.
The amount of atmospheric nitrogen (N) deposited on the land surface has increased globally and by nearly five times in China from 1901 to 2005. Little is known about how elevated reactive N input has affected the carbon (C) sequestration capability of China's terrestrial ecosystems, largely due to the lack of reliable data on N deposition. Here we have used a newly developed data set of historical N deposition at a spatial resolution of 10 km x 10 km in combination with other gridded historical information on climate, atmospheric composition, land use, and land management practices to drive a process-based ecosystem model, the dynamic land ecosystem model (DLEM) for examining how increasing N deposition and its interactions with other environmental changes have affected C fluxes and storage in China's terrestrial ecosystems during 1901-2005. Our model simulations indicate that increased N deposition has resulted in a net C sink of 62 Tg C/yr (1 Tg = 1012 g) in China's terrestrial ecosystems, totaling up to 6.51 Pg C (1 Pg = 10(15) g) in the past 105 years. During the study period, the N-induced C sequestration can compensate for more than 25% of fossil-fuel CO2 emission from China. The largest C sink was found in southeast China, a region that experienced the most significant increase of N deposition in the period 1901-2005. However, the net primary productivity induced by per-unit N deposition (referred to as ecosystem N use efficiency, ENUE, in this paper) has leveled off or declined since the 1980s. This indicates that part of the deposited N may not be invested to stimulate plant growth, but instead leave the ecosystem by various pathways. Except shrubland and northwest/southwest China, signs of N saturation are apparent in the rest major biome types and regions, with ENUE peaking in the 1980s and leveling off or declining thereafter. Therefore, to minimize the excessive N pollution while keeping the N-stimulated C uptake in China's terrestrial ecosystems, optimized management practices should be taken to increase N use efficiency rather than to keep raising N input level in the near future.
大气氮（N）在地表的沉积量在全球范围内增加，自 1901 年至 2005 年期间，中国的沉积量增加了近五倍。人们对增加的活性氮输入如何影响中国陆地生态系统的碳（C）固存能力知之甚少，主要是因为缺乏可靠的氮沉积数据。在这里，我们利用新开发的空间分辨率为 10 公里 x 10 公里的历史氮沉积数据集，结合其他关于气候、大气成分、土地利用和土地管理实践的网格化历史信息，驱动一个基于过程的生态系统模型，即动态陆地生态系统模型（DLEM），以研究在 1901-2005 年期间，增加的氮沉积及其与其他环境变化的相互作用如何影响中国陆地生态系统的 C 通量和储存。我们的模型模拟表明，增加的氮沉积导致中国陆地生态系统的净碳汇为 62TgC/yr（1Tg=1012g），在过去的 105 年中总计达到 6.51PgC（1Pg=1015g）。在研究期间，氮引起的碳固存可以补偿中国化石燃料 CO2排放的 25%以上。最大的碳汇出现在中国东南部，该地区是 1901-2005 年期间氮沉积增加最多的地区。然而，单位氮沉积引起的净初级生产力（本文中称为生态系统氮利用效率，ENUE）自 20 世纪 80 年代以来已经趋于平稳或下降。这表明部分沉积的氮可能不会用于刺激植物生长，而是通过各种途径离开生态系统。除了灌丛和中国西北部/西南部，其他主要生物群落类型和地区都出现了氮饱和的迹象，ENUE 在 20 世纪 80 年代达到峰值，此后趋于平稳或下降。因此，为了在保持中国陆地生态系统氮刺激的碳吸收的同时最小化过度的氮污染，应采取优化管理措施来提高氮利用效率，而不是在不久的将来继续提高氮输入水平。
