# Effects of Aerosols on Gross Primary Production from Ecosystems to the Globe
## 5 Conclusions  
The relationship between aerosols and diffuse radiation was quantified and a new LUE model developed in this study to explicitly account for the diffuse fertilization effect of aerosols on GPP. By changing the structure of the widely used EC-LUE model, the maximum LUE of diffuse PAR and direct PAR were incorporated and parameterized. In comparison with the original model (EC-LUE), the new model (AOD-LUE) shows fairly good performance across different biomes (R\({}^{2}\) = 0.68, \(p\) < 0.01). The model was then used to simulate GPP at the global level from 2000-2014. We then used the AOD-LUE model to simulate GPP at the global scale for the period 2000-2014. With the global-scale GPP estimates, we quantified the effects of aerosol radiation on GPP regionally and globally and for different vegetation types. Although the total effect is low, it still needs attention, because the total effect is offset by both positive and negative aspects, but the positive and negative effects of different regions are very large. Aerosols mainly have a relatively large negative impact on Closed Shrub (CSH) (\(\Delta\)GPP = \(-\)6.45%), and a positive impact on arid and semi-arid regions (GRA) (\(\Delta\)GPP = 3.19%) in the subtropical zone. Our results showed that the effects of aerosol radiation have severely affected the global GPP. Separating PAR to diffuse and direct components and incorporating their relative effects to LUE models are effective for improving the accuracy of the GPP simulation at regional to global scales. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/rs14122759/s1](https://www.mdpi.com/article/10.3390/rs14122759/s1)]([https://www.mdpi.com/article/10.3390/rs14122759/s1](https://www.mdpi.com/article/10.3390/rs14122759/s1)), Figure S1: Spatial pattern of global GPP simulated by the AOD-LUE model during 2000-2019: (a) averaged annual GPP; (b) trend of annual GPP (g C m\({}^{-2}\) yr\({}^{-1}\)); Table S1: Information of the eddy covariance (EC) sites used in this study for model calibration and validation. [PERSON] designed the research; [PERSON]. ([PERSON]), [PERSON] performed research; and [PERSON] ([PERSON]), [PERSON], [PERSON], [PERSON], [PERSON] ([PERSON]), [PERSON], [PERSON], [PERSON], [PERSON] ([PERSON]), [PERSON] ([PERSON]), [PERSON] and [PERSON] contributed to the writing of the paper. All authors have read and agreed to the published version of the manuscript. This research was funded by the National Natural Science Foundation of China (Grants No. 41971152 and U20A2089); and the Hunan Innovative Talent Program (Grant No. 2019 RS1062) to S.L. The FLUXNET2015 dataset (Available online: [[http://www.fluxdata.org](http://www.fluxdata.org)]([http://www.fluxdata.org](http://www.fluxdata.org)), accessed on 11 March 11 2020). The aerosol optical depths (AOD) for 550-nm wavelengths are available from the Office of Global Modeling and Assimilation (GMAO) of NASA (Available online: [[https://disc.gsfc.nasa.gov/datasets/](https://disc.gsfc.nasa.gov/datasets/)]([https://disc.gsfc.nasa.gov/datasets/](https://disc.gsfc.nasa.gov/datasets/)), accessed on 14 July 2021). The CERES PAR data are available online (Available online: [[https://ceres-tool.larc.nasa.gov/ord-tool/jsp/SYNldegEd41](https://ceres-tool.larc.nasa.gov/ord-tool/jsp/SYNldegEd41) Selection.jsp]([https://ceres-tool.larc.nasa.gov/ord-tool/jsp/SYNldegEd41](https://ceres-tool.larc.nasa.gov/ord-tool/jsp/SYNldegEd41) Selection.jsp), accessed on 3 May 2021). The global potential natural vegetation (PNV) map at 1 km spatial resolution (Available online: [[https://doi.org/10.7910/DVN/QQHCIK](https://doi.org/10.7910/DVN/QQHCIK)]([https://doi.org/10.7910/DVN/QQHCIK](https://doi.org/10.7910/DVN/QQHCIK)), accessed on 18 February 18 2021). The project was supported by the research grants from the National Natural Science Foundation of China (U20A2089 and 41971152) and Hunan Innovative Talent Program (2019 RS1062) to [PERSON].