高浓度CO2对树木生理生态的影响研究进展

大气CO2浓度升高已成为世界范围内的重要环境问题。CO2浓度升高势必会对植物的生理生态变化产生重要影响。综述了国内外有关高浓度CO2对树木生理生态影响研究的最新进展,具体包括高浓度CO2对树木生长发育、光合和呼吸作用、抗氧化系统、树木代谢物质、挥发性有机化合物以及树木凋落物等方面的影响。高浓度CO2一般会促进树木地上植株的生长和发育,但也因树种差异而有所不同。最新研究表明,高浓度CO2促进了树木细根周转,树木根系生长在大气CO2浓度升高条件下表现为促进作用,这种作用加快了全球森林生态系统的C循环。高浓度CO2虽然在一定程度上促进树木光合速率的增加,但长期熏蒸也往往会发生光合驯化,这种现象产生的生理学机制目前仍无定论。高浓度CO2对树木呼吸作用尤其是根系呼吸的影响将是未来研究的重点和难点。高浓度CO2一般会提高树木抗氧化酶活性与抗氧化剂含量,但不同树种响应高浓度CO2的过程和机理也有所差异。研究表明,高浓度CO2一般对树木凋落物的分解产生不利影响,但也因树种而异。需要强调的是,目前关于树木地下部分、树木对高浓度CO2的适应机理和重要过程(碳氮水耦合及基因调控等)以及多个树种包括不同类型树种及不同品种之间比较研究较少;关于某一重要生理生态机制(如根系生理代谢)尤其是多个生态因子复合条件下缺乏长期深入的研究。在此基础上给出了大气CO2浓度升高下树木生理生态学研究的未来发展方向,包括高CO2浓度条件下树木根系生理代谢及机制、树木碳氮水耦合的生理过程及机制、不同生态因子复合作用对树木生理影响机制以及树木分子作用机理等方面的研究。这些研究不仅将丰富森林树木应对未来气候变化的有关科学理论,也为全球气候变化背景下实现森林树种生态功能的优化选择及森林生态系统的可持续发展与经营提供重要的生理生态学理论依据和参考。

Research advance in effect of elevated CO2 on eco-physiology of trees

Rising atmospheric CO₂ concentration has been regarded as a key global environmental problem today: it is expected to influence changes in plant eco-physiology. The research advances on the effects of elevated CO₂ concentration on tree eco-physiology were reviewed: this included the effects of elevated CO₂ on growth and development, photosynthesis and respiration, antioxidative systems, volatile organic compounds (VOCs), and litter decomposition of trees. Generally, elevated CO₂ enhances the growth and development of trees and the results vary with tree species. The turnover in fine roots of trees was accelerated by elevated CO₂, which may play an important role in the cycle of global carbon in forest ecosystems. Elevated CO₂ increases net photosynthetic rate for most tree species. However, photosynthetic acclimation in some tree species sometimes occurred under elevated CO₂ concentrations, and it was still uncertain as to whether it revealed the physiological mechanism underpinning the occurrence of photosynthetic acclimation of trees to date. The effect of elevated CO₂ on root respiration of trees will be an important aspect of the study of forest ecosystems under a changing climate. The activities of antioxidative enzymes and the contents of antioxidants in trees were generally maintained at high levels under elevated CO₂ concentrations. The process and mechanism of antioxidative system response to elevated CO₂ concentration were associated with certain tree species. Although the adverse effect of elevated CO₂ on the decomposition of tree litter has been observed in recent studies, it also depends on tree species. Numerous studies were focused on the apparent physiological responses of trees to elevated CO₂. However, little is known about the physiological processes including coupling of carbon, nitrogen, and water, or gene regulation under elevated CO₂ concentrations, particularly in the underground parts of trees. Many studies have been carried out based on individual plant levels, but there has been a lack of comparative studies of the response of different tree species or varieties to elevated CO₂ concentrations. Little information exists about the long-term study of the key processes and mechanisms of physiological metabolism of fine roots under the action of multiple environmental factors. The perspectives in studies of tree eco-physiology under elevated CO₂ concentrations were summarized, including research into the physiological mechanisms of tree root metabolism, coupling in carbon, nitrogen and water processes, responses and adaptations to multiple environmental factors, and related molecular mechanisms under elevated CO₂ concentrations. This research will enrich the knowledge relating to the responses and adaptations of forest trees to climate change, especially for the sustainable management and operation of forest eco-systems and the selection of tree species.