# Spatiotemporal Evolution and Impact Mechanisms of Gross Primary Productivity in Tropics
## Discussion
### Climate and Land Cover Regulation of GPP in the Tropics  
GPP changes in the tropics are influenced by a combination of temperature and precipitation factors, but precipitation is the main driver affecting GPP changes overall, consistent with the findings of [PERSON] et al. [15]. In coastal areas, GPP was positively correlated with temperature and negatively correlated with precipitation, while in inland areas, the opposite was true. This may be due to the fact that inland areas are relatively drier and plant growth is limited by precipitation, while high temperatures accelerate the rate of water transpiration; conversely, in coastal areas, where precipitation is abundant, temperature becomes the limiting factor for growth. The partial correlation between vegetation GPP and precipitation in the tropics was more significant than that of temperature, indicating that precipitation conditions predominated the growth of vegetation GPP in the tropics among the two climatic factors of temperature and precipitation. In general, the vast majority of the tropical region has high temperatures throughout the year, and changes in temperature have a relatively small impact on vegetation growth; meanwhile, the precipitation factor, with its differences in spatial and temporal distribution, is the main factor affecting GPP. [PERSON] et al. showed that in arid and tropical regions [19], vegetation productivity is usually limited by water availability. In contrast, high temperatures extend the length of the growing season, thereby increasing vegetation productivity. However, high temperatures also promote evapotranspiration, which may lead to severe water loss and inhibit the growth of vegetation productivity. The inland areas of the tropics are more arid, and the influencing factors of vegetation GPP changes are similar to the findings of [PERSON] et al. [51], [PERSON] et al. [52], and [PERSON] et al. [53], indicating precipitation is the main regulator of GPP changes in the arid region, whereas the coastal areas are more humid, and the results of the study are similar to those of [PERSON] et al. [54] and [PERSON] et al. [55], indicating the GPP changes in the humid region are mainly regulated by air temperature. In the wet region, increased precipitation led to both insufficient sunshine hours and temperature conditions as well as the root system of vegetation being soaked by water and unable to carry out aerobic respiration, thus affecting the efficiency of nutrient and water uptake and limiting the growth and development of the vegetation. [PERSON] et al. showed that [56] in the more arid region (the precipitation in the growing season was less than 200 mm), the aboveground biomass was negatively correlated with the temperature, while in the wet region (the precipitation in the growing season was less than 200 mm), the aboveground biomass was negatively correlated with the temperature. wetter areas (growing season precipitation over 200 mm), aboveground biomass was weakly positively correlated with temperature, which was consistent with the results of this experiment. Land cover change plays a major role in GPP change [15]. The areas in the tropics where land cover change is the main driver are deciduous coniferous forest, tree mixed, and urban areas, mostly distributed in the central part of South America, central and southeastern Africa, and Madagascar Island, while the rest of the areas are more affected by climatic factors. [PERSON] et al. 's results showed that the largest negative effect on GPP change comes from land cover change [15], and these negatively affected areas are concentrated in South America, Eurasian tropical rainforests, and tropical dry forests in Africa, i.e., the central part of South America and Africa, as well as Southeast Asia. [PERSON] et al. showed that land cover change has a more significant negative impact on GPP in southeastern South America [57], eastern and central Africa, and the Indian Peninsula, and in Southeast Asia, on the other hand, showed a slight positive impact.