Impacts of Cloudiness and Anthropogenic Aerosols on the Net Ecosystem Carbon Exchange of Forest Ecosystems in China

Changes in the surface solar radiation caused by climate change and by anthropogenic aerosol loading changes can impact forest ecosystem carbon uptake. In this study, we investigated the impacts of cloudiness and anthropogenic aerosol loading on forest ecosystem net carbon uptake. Our study sites consisted of three forest ecosystems along the North-South Transect of Eastern China from the north to the south: the Changbaishan temperate mixed forest (CBS), the Qianyanzhou subtropical coniferous plantation (QYZ), and the Dinghushan subtropical evergreen broad-leaved forest (DHS). The analysis was based on the measured net ecosystem exchange of CO2 (NEE), microclimate data, and aerosol optical depth (AOD) data. We found that the mid-growing season (June – August) NEE reached its maximum when the clearness index was about 0.5 in the three forest ecosystems. The result indicates that increase in diffuse radiation under cloudy sky and aerosol loading increasing conditions was beneficial to forest growth. Under clear sky conditions, the mid-growing season NEE became more negative with increasing AOD, or in other words, increasing AOD resulted in higher carbon uptake of these forests. Furthermore, DHS showed higher sensitivity to AOD than CBS and QYZ.