# Estimating Global Gross Primary Production Using an Improved MODIS Leaf Area Index Dataset  
[PERSON]  
1 College of Geography and Environmental Science, Henan University, Kaideng 475004, China; [EMAIL_ADDRESS] (S.W. ); [EMAIL_ADDRESS] (C.Z. ); [EMAIL_ADDRESS] (L.H.) [PERSON]  
1 College of Geography and Environmental Science, Henan University, Kaideng 475004, China; [EMAIL_ADDRESS] (S.W. ); [EMAIL_ADDRESS] (C.Z. ); [EMAIL_ADDRESS] (L.H.) [PERSON]  
1 College of Geography and Environmental Science, Henan University, Kaideng 475004, China; [EMAIL_ADDRESS] (S.W. ); [EMAIL_ADDRESS] (C.Z. ); [EMAIL_ADDRESS] (L.H.) [PERSON]  
2 Guangdong-Hong Kong Joint Laboratory for Carbon Neutrality, Jiangmen Laboratory of Carbon Science and Technology, Jiangmen 529199, China; [EMAIL_ADDRESS]  
[PERSON]  
1 College of Geography and Environmental Science, Henan University, Kaideng 475004, China; [EMAIL_ADDRESS] (S.W. ); [EMAIL_ADDRESS] (C.Z. ); [EMAIL_ADDRESS] (L.H.) Footnote 1: [[https://www.mdpi.com/journal/remotesensing](https://www.mdpi.com/journal/remotesensing)]([https://www.mdpi.com/journal/remotesensing](https://www.mdpi.com/journal/remotesensing))  
Footnote 2: [[https://www.mdpi.com/](https://www.mdpi.com/)]([https://www.mdpi.com/](https://www.mdpi.com/))  
physics. These models have facilitated a deeper understanding and explanation of the biological mechanisms underlying photosynthesis. GPP product information can be found in Table 1.  
The global distribution of C3 and C4 plants manifests distinct efficiencies in the assimilation of CO2 during photosynthesis, altering the regional atmospheric CO2 concentration and isotopic composition, thereby impacting the global carbon cycle [17]. Studies have revealed that C3 plants predominantly govern carbon absorption and GPP in temperate and high-latitude regions, whereas C4 plants assume significance in tropical and subtropical regions [18; 19]. The distribution and influence of these two plant species might change considerably with climate change. C4 plants could expand their distribution and influence to more areas (including some traditional C3 plant areas), which could alter the carbon cycle and influence of these areas and, thus, affect the global carbon cycle and ecosystem productivity [17; 20; 21; 22]. The nitrogen content in leaves influences the active amount and kinetic activity of RuBisCO, as well as the temperature-standardized rate of maximum RuBisCO carboxylation (V\({}_{\text{cmax25}}\)), thereby affecting the rate of plant photosynthesis [23].The terrestrial carbon cycle model is highly sensitive to the maximum carboxylation rate (V\({}_{\text{cmax}}\)) and the maximum electron transport rate (J\({}_{\text{max}}\)) derived from V\({}_{\text{cmax25}}\) during photosynthesis, which are influenced by leaf nitrogen content and plant nitrogen uptake [24]. However, current ecological models only couple the C3/C4 plant processes in the Community Land Model (CLM) and do not generate data products. Consequently, it is necessary to develop a model that can quickly and stably estimate global GPP on a large scale while coupling the C3/C4 processes and leaf nitrogen content with photosynthesis so as to reduce significant errors in the estimation of global GPP caused by current models. The model we developed is driven by the leaf area index (LAI), distinguishes between C3 and C4 plants, optimizes the effects of nitrogen content on V\({}_{\text{cmax}}\) and J\({}_{\text{max}}\), and captures the physical and chemical information of the surface, improving the accuracy of GPP simulation. This study aims to (1) develop a moderate-resolution GPP dataset with a spatial resolution of 0.1 degree and a temporal resolution of one day, (2) use the above model to estimate the global GPP from 2000 to 2022, and (3) identify the key drivers of global annual GPP.