气溶胶及其与降水格局变化的交互作用对植物碳吸收、碳分配及水分利用效率的影响

Aerosols could alter ecosystem carbon and water cycles through the following three processes: 1) Aerosol often increases the amount of diffuse radiation, which will increase canopy light use efficiency, and therefore the ability of ecosystem to uptake carbon dioxide. However, heavy aerosol loadings could result in great reductions in photosynthetically active radiation, which will decrease ecosystem carbon uptake by inducing a light limitation; 2) Aerosol could alter transpiration by changing stomatal conductance, leaf temperature and vapor pressure deficit, which could alter water use efficiency at both leaf and ecosystem scale; 3) Aerosol leads to a great reduction in solar radiation reaching the surface, which could slow regional and global hydrological cycle. Increase in aerosol loadings also increase the droplet number concentration and the amount and lifetime of cloud, which eventually suppress precipitation. How anthropogenic aerosol affects carbon and water cycles will greatly affect the capability of ecosystems to moderate and adapt to climate changes. However, because of lacking of field experiments, especially at leaf and plant level, our knowledge on aerosol’s effects on carbon and water cycle is far from being complete.The goal of the proposed study is to investigate how the interaction of increasing aerosol loading and changing precipitation regime will affect carbon and water cycles at leaf and plant level. We will choose a clean and a polluted site along the urban-rural aerosol gradient, and use same manipulation protocol to simulate precipitation regime change at both sites. Leaf photosynthesis, water use efficiency, and belowground carbon cycle will be measured at each site. Our research will provide information on how anthropogenic aerosol affects ecosystem carbon and water cycles in the setting of climate change, which will help us to better evaluate the ability of ecosystems to respond and adapt air pollution and climate change.

气溶胶可通过以下过程影响碳水循环：（1）增加散射辐射比率，提高冠层光利用效率，从而促进生态系统碳吸收。但气溶胶浓度过高时，其对总辐射的削减会抑制生态系统碳吸收；（2）改变气孔导度、叶片温度等，影响蒸腾作用，从而改变叶片及生态系统水分利用效率；（3）影响辐射及成云过程，改变区域降雨量及降雨频率。气溶胶及其与降水格局变化的交互作用如何影响碳水循环，关系到生态系统对气候变化的响应和适应能力。然而由于缺乏叶片及个体尺度的野外实验研究，我们对碳水循环如何响应气溶胶与降水格局变化的生理机制的认识还很薄弱。本研究拟利用城郊气溶胶梯度，结合降水控制实验，通过对光合作用、蒸腾作用、地下碳循环等过程的监测，探讨气溶胶与降水格局变化的交互作用如何影响叶片及个体的碳吸收、分配及水分利用。本研究将有望推动气候变化背景下气溶胶对生态系统碳水循环影响机制的认识，为评估生态系统对气溶胶及气候变化的响应与适应提供科学依据。

气溶胶可通过增加散射辐射比率，提高冠层光利用效率，从而促进生态系统碳吸收。但气溶胶浓度过高时，其对总辐射的削减会抑制生态系统碳吸收；气溶胶浓度上升也会改变气孔导度、叶片温度等，影响蒸腾作用，从而改变叶片及生态系统水分利用效率。气溶胶及其与环境水分条件变化的交互作用如何影响碳水循环，关系到生态系统对气候变化的响应和适应能力。然而由于缺乏叶片及个体尺度的野外实验研究，我们对碳水循环如何响应气溶胶与降水格局变化的生理机制的认识还很薄弱。本项目利用城郊气溶胶梯度，对植物生理、环境气象条件和其他大气污染物浓度进行了四年的监测，对气溶胶及水分环境变化如何影响叶片和冠层尺度的光合作用、蒸腾作用等过程进行了系统的研究。取得了以下五个方面的成果（1）阐明了高气溶胶天气下辐射和大气水分亏缺变化对杨树叶片光合及茎干生长的影响机制；（2）发现气溶胶中的含氮化合物沉降后，能被林冠层直接吸收，并促进叶片光合上升；（3）量化了复合污染条件下，气溶胶、臭氧和大气氮沉降对树木生长影响的贡献；（4）揭示了大气气溶胶浓度变化对杨树叶片和个体尺度上水分利用的影响及相关机制；（5）探讨了气溶胶浓度变化对地下碳循环的潜在影响，发现高气溶胶浓度下土壤温度上升，从而促进了土壤呼吸。这些发现帮助我们进一步了解了气候变化背景下气溶胶对生态系统碳水循环的影响机制，为评估生态系统对气溶胶及气候变化的响应与适应提供科学依据。相关成果发表在Global Change Biology、New Phytologist、Environmental Pollution、《植物生态学报》等刊物。