Intermediate Aerosol Loading Enhances Photosynthetic Activity of Croplands. Issue 7 (1st April 2021) - Wang, Xin
Abstract: Aerosols can affect crop photosynthesis by altering radiation and meteorological conditions. By combining field observations, mechanistic modeling, and satellite‐retrieved solar‐induced chlorophyll fluorescence (SIF), we assessed aerosols' impacts on crop photosynthesis from leaf to regional scale. We found that the initial increase in aerosol optical depth (AOD) enhanced photosynthesis of sun leaves, shade leaves, and canopy, which reached their maximum at AOD = 0.76, 1.13, and 0.93, respectively, and then decreased. Aerosol‐induced changes in radiation regime and the concurrent high relative humidity led to such nonlinear responses. Similarly, the SIF of croplands in the North China Plain (NCP) also showed a bell‐shaped response to aerosols. The optimal AOD level at which SIF reached the maximum value varied from 0.56 to 1.04, depending on the background meteorological conditions. Approximately 76%–90% of the NCP exceeded the optimal AOD level, suggesting that stringent aerosol pollution control could promote cropland productivity in this region. Plain Language Summary: High aerosol loading could produce either a positive or negative impact on crop photosynthesis. However, experimental tools for manipulating aerosol loading in the field are lacking, creating significant uncertainty in assessing the impact of aerosols on crop yields. The cyclical fluctuations in aerosol loading in the North China Plain (NCP) provide a unique opportunity to study aerosols' effect on crop productivity. We found that the photosynthesis of sun and shade leaves and canopy reached their maximum at a moderate level of aerosol loading. Similarly, satellite‐observed solar‐induced chlorophyll fluorescence across the NCP also demonstrated that intermediate aerosols enhance crop photosynthesis at regional scales. The further analysis indicated that the changes in direct and diffuse radiation and the concurrent high air humidity together led to the nonlinear response of soybean photosynthesis to aerosol loading. Our findings suggested that stringent aerosol pollution control will increase crop productivity in the NCP. Key Points: Soybean sun and shade leaf photosynthesis show a quadratic response to aerosols, peaking at aerosol optical depth of 0.76 and 1.13, respectively The changes in radiation regimes and concurrent high relative humidity lead to such nonlinear responses of leaf photosynthesis Solar‐induced chlorophyll fluorescence in the North China Plain also demonstrate that intermediate aerosols enhance crop photosynthesis