# Comprehensive Effects of Atmosphere and Soil Drying on
## 1 Introduction  
Vapor pressure deficit (VPD) and soil water content (SWC) are two important environmental factors that influence vegetation photosynthetic efficiency, gross primary productivity (GPP), and net primary productivity (NPP) [1, 2]. Photosynthesis is the primary pathway for vegetation to obtain energy and organic matter, absorbing carbon dioxide through the stomata while releasing water vapor during the transpiration process. GPP refers to the total amount of solar energy fixed by plants through photosynthesis, including the energy used in biochemical reactions and the energy lost during photosynthesis. NPP, on the other hand, is the remaining energy after subtracting the energy used for plant growth and reproduction from GPP. Thus, GPP represents the total energy obtained by plants through photosynthesis, while NPP represents the net energy used for growth and reproduction. Sufficient soil moisture provides the necessary water supply for vegetation, allowing for optimal water uptake through roots for photosynthesis and biomass accumulation. However, a decrease in SWC leads to a decrease in the available water taken in by plant roots [3]. Insufficient soil moisture can have negative impacts on vegetation productivity, limiting photosynthesis and biomass accumulation, leading to decreased GPP and NPP [4; 5], while an increase in VPD will induce plants to close stomata to minimize leaf-scale water loss and further inhibit plant photosynthesis in the ecosystem [6; 7], and lower photosynthetic efficiency usually indicates reduced utilization of light energy for photosynthesis and lower production of organic matter. This is because plants need to adjust stomatal conductance to maximize carbon gains and reduce water loss as much as possible under the condition of high VPD. Evidently, this process will affect the carbon cycle and water cycle of the ecosystem [8; 9]. Vegetation water use efficiency (WUE) and carbon use efficiency (CUE) are important parameters that describe how plants utilize water and carbon during photosynthesis. Vegetation water use efficiency refers to the amount of water required by plants to produce a unit of biomass during photosynthesis, while carbon use efficiency refers to the amount of carbon fixed through photosynthesis that is allocated to plant growth and reproduction [10; 11]. There is a complex relationship between GPP, NPP, photosynthesis, vegetation water use efficiency, and carbon use efficiency. Higher GPP and NPP are generally associated with higher photosynthesis rates, as more solar energy is captured and converted into organic matter. This may result in higher vegetation water use efficiency, as plants can produce more biomass with less water. Similarly, higher carbon use efficiency may be observed, as more carbon is allocated to plant growth and reproduction [12]. In recent years, many studies have emphasized the importance of VPD and SWC on plant stomatal conductance (Gs) and evaluated their sensitivity and contributions. [PERSON] et al. [13] found that in many biomes, VPD had greater restrictions on stomatal conductance (Gs) and evapotranspiration (ET) than SWC. In the future, the impact of atmospheric demand on vegetation function will become more and more important, accounting for more than 70% of the surface conductance limit in the growing season of temperate forests. [PERSON] et al. [14] showed that ecosystem-scale transpiration and photosynthesis were significantly correlated with VPD and SWC, and VPD was the main contributor to the interannual changes in photosynthesis and transpiration in temperate forest sites. The analysis of crops also showed that the Gs difference was mainly due to the change in VPD, which was almost unrelated to the changes in environmental conditions (rainfall and temperature gradient), crop types (corn and soybean), and management practices (irrigated or not) [15]. In addition, plant water use efficiency (WUE) is also affected by VPD and SWC.