气候变暖对陆地生态系统碳循环的影响

作为全球变化的主要表现之一,气候变暖对全球陆地生态系统碳循环的影响巨大,揭示这一作用对于精确理解碳循环的过程和相关政策的制定具有重要的指导意义。该文综述了此领域近十几年来的主要研究工作,总结了陆地生态系统碳循环对气候变暖响应的主要内部机制及其过程,简述了相关模型的发展及其主要应用,并指出以往研究中存在的主要问题以及未来研究的主要方向。在气候变暖条件下,陆地生态系统碳循环的变化主要体现在以下几个方面:1)低纬度地区生态系统NPP一般表现为降低,而在中高纬度地区通常表现为增加,而在全球尺度上表现为NPP增加;2)土壤呼吸作用增强,但经过一段时间后表现出一定的适应性;3)高纬度地区的生态系统植被碳库表现为增加趋势,低纬度地区生态系统植被碳库变化不大,或略微降低,在全球尺度上表现为植被碳库增加;4)地表凋落物的产量和分解速率增加;5)土壤有机碳分解加速,进而减少土壤碳储存,同时植被碳库向土壤碳库的流动增加从而增加土壤碳库,这两种作用在不同生态系统的比重不同,在全球尺度上表现为土壤碳库的减少;6)尽管不同生态系统表现各异,总体上全球陆地生态系统表现为一个弱碳源。生物物理模型、生物地理模型和生物地球化学模型陆续被开发出来用于研究工作,并取得了一定的成果,但是研究结果仍然存在很大的不确定性。在未来的数年甚至是数十年间,气候变暖与全球变化的其它表现间的协同影响将是下一步的研究重点,气候变暖和陆地生态系统间的双向反馈作用机制是进行更准确研究的理论基础,生态系统结构和功能对气候变化的适应性是准确理解和预测未来气候情景下陆地生态系统碳循环的前提。

CLIMATE WARMING IMPACTS ON CARBON CYCLING IN TERRESTRIAL ECOSYSTEMS

Climate warming is one key issue of global change and plays an important role on carbon cycling in terrestrial ecosystems. This paper reviews the recent advance in our understanding of global warming and its impacts on terrestrial carbon cycling and underlying mechanisms. We also discuss the state-of-the art in ecosystem modeling and its applications to ecosystem assessment. Climate warming will influence terrestrial carbon cycling in several aspects: 1) net primary productivity (NPP) will decrease in low-latitude region, and increase in mid-and high-latitude zones, totally show an increase on the global scale; 2) soil respiration will increase at the initial stage and then keep relatively stable because of biotic adaptability; 3) plant carbon storage will increase in high-latitude region, and remain stable or even decrease in low-latitude zone, and show a s light increase on the global level; 4) the production and decomposition rate of litterfall will increase; 5) the decomposition rate of soil organic carbon will increase and thus decrease soil carbon stock, meanwhile, soil carbon stock will increase for more carbon input from plant litter. These two processes will trade off in certain degree, resulting in different results for varied ecosystems. On the global scale, soil carbon stock will show a decrease; 6) although the different performances of diverse ecosystems, the global terrestrial ecosystem acts as a weak carbon source. Biophysical, biogeographical and biogeochemical models were developed in the past decades for global change research. In the future research, there are an urgent need to address the interaction among climate warming and other factors including elevated CO₂, O₃, drought, fire disturbance. The big challenge we are facing is how to deal with the complexity with multi-factors and multi-scales by using experimental and modeling approaches.