Effects Of Aerosols On Photosynthetically Active Radiation And Plant Gross Primary Productivity

Accurate estimation of(gross primary productivity)GPP on the global scale is essential for understanding the global carbon cycle and predicting future climate change.Atmospheric aerosols will promote plant growth by increasing the Diffuse Fraction(Df)of Photosynthetically Active Radiation(PAR),thereby increasing the uncertainty of the simulation of GPP.Therefore,the quantitative analysis of the relationship between aerosol optical depth(AOD)and diffusion rate(aerosol diffusion fertilization effect)on the global primary productivity has become a hot topic in the world.In this study,a new model(AOD-LUE model)including the influence of aerosols was generated by modifying the original light energy utilization efficiency model(EC-LUE model).The new model changes the structure of PAR and separates it into direct PAR and diffuse PAR,and obtains the light use efficiency(LUE)under the conditions of diffuse PAR and direct PAR.In order to test the applicability of the AOD-LUE model,this study uses the FLUXNET2015 data set covering 70 flux site measurement data of 10 main ecosystem types to calibrate and verify the AOD-LUE model.The AOD-LUE model is used to simulate GPP on a global scale,and a GPP data set with a spatial resolution of 0.1°×0.1° and a time scale of 1 m from 2000 to 2019 is obtained.At the same time quantify the specific contribution of aerosols to the global GPP.The main findings are as follows:(1)Aerosols and diffuse PAR show highly similar distribution patterns and growth trends in the temporal and spatial distribution,while direct PAR and total PAR show opposite distribution trends.On the time scale,aerosol and diffuse PAR showed a slight upward trend as a whole,while the other two radiations showed a slight downward trend.(2)The global radiation diffuse fraction(Df)increases with the increase of aerosol concentration,and has a significant positive correlation(R2=0.57,p<0.01),but when the diffusion rate reaches 0.6,the aerosol will not have an impact on it.(3)Model optimization results show that the light use efficiency(LUE)(3.61 g C m-2 MJ-1)of vegetation under diffuse radiation conditions is much higher than that of direct radiation(1.68 g C m-2 MJ-1).(4)Considering the relationship between diffuse fraction and aerosols,through parameter optimization,the accuracy of the GPP model at each site has been improved.Among different vegetation types,closed shrubs and evergreen deciduous broad-leaved forests had the largest increase in R2,which was 60%and 28%,respectively.(5)On a global scale,aerosols have positive and negative effects on GPP(g C m-2 yr-1),and the positive effects are mainly distributed in subtropical areas,while there are significant negative effects in tropical areas.In the biome,the most adversely affected area is the tropical rain forest,which will reduce the GPP(g C m-2 yr-1)by an average of 9.24%.The steppe shows a positive effect,increasing the GPP(g C m-2 yr-1)by 3.19%on average.In this study,a new GPP model was developed on the basis of correcting the original data-and optimizing the structure and parameters of the model by evaluating the uncertainty of the aerosol radiation effect on the global GPP simulation.And based on the new model AOD-LUE to generate long-term global GPP products affected by aerosols,reveal the important role of aerosols in GPP simulation,and reflect the changing trend of global GPP.This research helps explain how aerosols affect plant physiological processes and provides the possibility for future GPP models to more accurately simulate the global carbon cycle.This research helps explain how aerosol radiation effects affect plant physiological processes,and provides theoretical basis and practical experience for future GPP models to more accurately simulate the global carbon cycle.