## 4 Discussion
### The Relationship between Meteorological Elements and GPP  
Temperature, precipitation, and radiation, among other meteorological elements, collectively influence vegetation growth and photosynthesis [56], consequently affecting vegetation's carbon absorption from the atmosphere and terrestrial carbon sequestration capacity. The primary way that solar radiation affects GPP is through light energy. Plants utilize chlorophyll in their leaves to absorb light energy, convert it into chemical energy, and use it for photosynthesis. Different wavelengths of radiation have varying effects on  
Figure 10: Statistical analysis of the lag phases in GPP response to meteorological elements in key land use-type regions (C, cropland; F, forest; G, grassland; B, barren land). chlorophyll absorption [57]. Under low light conditions, where light saturation is high, plants can efficiently utilize more light energy to increase photosynthesis rates. However, under high light conditions, light saturation gradually decreases, and the photosynthesis rate of plants no longer increases with the increasing light, thereby limiting their carbon absorption capacity. Therefore, higher light intensity is generally beneficial for increasing the photosynthesis rate of plants and enhancing their carbon absorption capacity. Temperature affects the growth and development process of plants, including seed germination, seedling growth, flowering, and fruiting [58]. Suitable temperature is beneficial for plant growth and improves GPP. Generally, photosynthesis rates increase with rising temperatures because temperature promotes the catalytic reactions of enzymes. This means that, at higher temperatures, plants can convert carbon dioxide (CO\({}_{2}\)) and water (H\({}_{2}\)O) into organic compounds more rapidly, thereby enhancing their carbon absorption capacity. For example, during the warm summer season, increased temperatures often lead to higher photosynthesis rates in plants, boosting vegetation's carbon absorption capacity. However, extreme heat or cold events can have a severe impact on vegetation, limiting photosynthesis rates and carbon absorption capacity [59]. High-temperature events can potentially deactivate photosynthetic enzymes, damage leaf tissues, and consequently reduce carbon absorption. In addition, temperature also affects the activity of soil microorganisms, which in turn affects the decomposition and cycling of soil nutrients, and ultimately affects GPP [60]. Rainfall provides the necessary water for plants, maintaining their water balance. Adequate water can promote photosynthesis in plants since water is one of the reactants in photosynthesis. For example, in tropical rainforests, where annual rainfall is abundant, plants often exhibit a high carbon absorption capacity [61]. These plants can efficiently utilize the ample rainfall for photosynthesis, resulting in substantial carbon absorption, thereby helping to maintain the carbon balance of the rainforest ecosystem. Conversely, insufficient rainfall or drought conditions can limit plants due to water stress [62]. Drought conditions can cause plants to close their stomata to reduce water loss, which restricts the entry of the carbon dioxide and reduces photosynthetic rates. Increased rainfall helps to alleviate water stress, promote vegetation restoration, and improve GPP. Furthermore, rainfall also brings nutrients such as nitrogen from the atmosphere into the soil, increasing soil nutrient content and providing more nutrients for plant growth [63]. The delayed response of vegetation to meteorological changes typically does not occur immediately but rather involves a certain time lag. This lag effect can offer several important benefits for ecosystems and the climate. Vegetation lag effects can enhance the stability and resilience of ecosystems [64]. When meteorological elements undergo short-term fluctuations or extreme events, vegetation does not respond abruptly but rather gradually adapts to the new conditions.