陆地碳平衡对大气CO_2升高的响应及其机制

Effects of CO_2-enrichment on the carbon balance of terrestrial ecosystems and the mechanisms

研究陆地碳平衡对大气CO2浓度升高的响应,能为揭示碳失汇之迷提供有力证据,为制定缓解全球变化的合理政策措施提供理论依据。综述了陆地碳平衡对全球大气CO2升高的响应及其可能的机制,由于陆地生态系统的复杂性,以及不同的研究在具体的对象、时间、地点、方法和角度的差异,目前有关陆地碳平衡对全球大气CO2升高的响应还存在很大的分歧。陆地碳库主要可分为植被碳库和土壤碳库,大气CO2浓度升高主要是通过影响光合作用、土壤养分、水分供应、光照条件、群落组成、光合产物分配等方式影响植被碳库;而土壤碳库的响应机理主要包括光合产物向土壤的输入量、脱落物质量、养分循环、光合产物分配、根系周转期、微生物活性等的响应。关于陆地碳平衡对全球大气CO2升高的响应今后应该主要集中在:(1)不同生态系统影响全球植被碳库变化的主导因子;(2)大气CO2浓度升高与其他环境因子的互作效应;(3)大气CO2浓度升高对植物光合作用的促进效应与光合作用适应性间的关系;(4)地上碳库与地下碳库间的相关性,及其对大气CO2浓度升高的分别响应;(5)克服目前实验方法存在的局限性。

During the past two centuries, the atmospheric carbon dioxide （CO2） concentration has increased by near 1/3 due to anthropogenic emissions. The response of carbon balance of the terrestrial ecosystems to elevated CO2 has gained attention, due to the two facts： 1） the worldwide plant will be around the environment of CO2-enrichment with the increasing concentration of CO2 in the atmosphere, and 2） the terrestrial carbon sink will be changed because of the direct effect of elevated CO2 on plant photosynthesis. Study on the relationship between atmospheric CO2-enrictunent and the carbon balance of terrestrial ecosystems could provide evidence on the conundrum of missing carbon sink, and could help government establish accurate and timely policies and measurements to mitigate the rising of atmospheric CO2 and thus to slow the rate of global climate change. The effects of CO2-enrichment on the carbon balance of terrestrial ecosystems and its possible mechanisms are reviewed in this paper. Numerous studies have generated significant knowledge about the response of terrestrial carbon sink to elevated CO2. However, because of the complex of terrestrial ecosystems and the differences in specific objects, times, sites, methods and aspects in different studies, there are disputes about these responses, which potentially constrain the generality of these results. Whether the sink will increase or the exact size and dynamics of this sink in the future remain uncertain. Terrestrial carbon sink mainly consisted by vegetation- and soil-sink. Through different approaches, CO2-enrichment influence vegetation- and soil-sink. The mechanisms for vegetation sink mainly include the responses of plant photosynthesis, soil nutrient, water supply, light condition, species composition and distribution of photosynthate among different organs to elevated CO2. While the effects of elevated CO2 on soil sink are mainly through influencing on photosynthate rate imported to soil, litter chemical composition and quality, nutrient circle, distribution of photosynthate among different organs, root mortality period and activity of microorganism. Further studies on the relationship between carbon balance of the terrestrial ecosystems and elevated CO2 should focus on 1） the predominant factors influencing the changing of global vegetation carbon sink, 2） the interactions between atmospheric CO2-enricment and other environmental conditions, 3） the controversies between the sustainability of plant photosynthesis enhancement responses and the importance of acclimation of photosynthesis to the atmospheric CO2-enrichment, 4） the relationship between the aboveground and belowground carbon sinks and their separating responses to atmospheric CO2-enrichment, and 5） the novel and more accurate methods that could conquer the limitations of current used methods.