Responses of vegetation photosynthetic processes to aerosol-induced direct radiative effect in China

Aerosols play an essential role in the energy cycle of land-atmosphere systems through interactions with radiation and clouds. Aerosol-induced direct radiative effect (ADRE) has a large effect on the photosynthetic processes of vegetation in terrestrial ecosystems. We used the Fu-Liou radiation transfer model integrated with the Community Land Model (CLM) to quantify ADRE and the responses of vegetation photosynthetic processes to ADRE in China from 2001 to 2014. The aerosols exhibited a positive effect on the diffuse fraction and it increased at first and decreased later. Positive impacts of ADRE on the leaf area index (LAI) of both sun (LAISUN) and shaded leaves (LAISHA) were captured in most areas of China, with increases of 0.01 and 0.09, respectively. The changes in LAI caused by ADRE were consistent with aerosol loading in northern and eastern China. In addition, due to the large decrease in total radiation caused by aerosols, ADRE reduced the photosynthetic rate of sun leaves. However, when the aerosol optical depth (AOD) ranged from 0.50 to 0.57, ADRE had positive effects on the photosynthetic rate of shaded leaves, and the AOD interval for positive impacts on the photosynthetic rate was different in each subregion of China. Mechanistic analysis found that ADRE could reduce the ribulose 1,5-bisphosphate (RuBP) carboxylase-limited rate of carboxylation and enhance the light-limited rate. When the AOD was around 0.47, the positive impacts of ADRE on the light-limited rate peaked throughout China (∼0.149 μmol m-2 s-1).