CO2浓度升高对森林碳平衡及碳氮耦合的影响

摘要

There are many uncertainties in the effects of elevated atmospheric CO2 concentration on the carbon balance of forest ecosystems and the C-N coupling mechanisms. Recent researches were focused on photosynthesis, productivity, litter decomposition and soil carbon pool of forest ecosystems in the temperate regions. The study results showed that CO2-enrichment (1) increased the photosynthesis of forest plants in the short-term, but photosynthetic acclimation would be observed in the long-term because of low supply of nitrogen and reductions in leaf nitrogen; ( 2) increased the net primary productivity ( NPP) of forest ecosystems and influenced the allocation of NPP in all components, but the sustained growth of NPP was limited by constant soil nitrogen mineralization rate and decreasing soil nitrogen availability; (3) increased the biomass of litter, stimulated microbial nitrogen absorption and assimilation, enhanced nitrogen use of plants, and thus influenced the process of litter decomposition; (4) increased soil carbon input and soil carbon sequestration but was restricted by low nitrogen availability and additional nutrients supporting nitrogen fixation. The environmental conditions of tropical and subtropical forests are very different from those of temperate forests, so in order to further investigate the effects of elevated CO2 on forest ecosystems, more attention should be paid to the studies in these regions.%森林碳平衡及碳氮耦合对大气CO2浓度升高的响应存在着诸多不确定性,现有研究主要集中在温带地区,并体现在光合作用、生产力及分配、枯落物分解以及土壤碳库等各个方面,研究结果表明:CO2浓度升高(1)短期内增强了森林的光合能力,长期条件下由于氮供应与叶氮含量的下降,就会产生光合下调与适应现象；(2)提高了森林净初级生产力(NPP)并影响其在各组分之间的分配,但却没有促进土壤氮矿化作用,土壤氮有效性降低,限制了森林NPP的持续上升；(3)增加了森林枯落物的数量,刺激了微生物的氮吸收与同化以及植物对有效氮的利用,从而影响分解过程；(4)增强了森林土壤的碳汇功能,但同样会受到氮有效性的直接限制与支持氮固定的其它养分的间接限制.由于热带、亚热带地区的环境因素与温带地区存在较大差异,未来应加强这些区域的相关研究,进一步揭示森林生态系统对CO2浓度升高的响应机制.