关键词: 草地生态系统, 净初级生产力, 空间分布, 气候因子, 非对称响应

Abstract:

Global climate change has increasingly affected terrestrial ecosystems. The occurrence of extreme events such as high temperatures and droughts poses challenges to ecosystem services and biodiversity. Grassland ecosystems store approximately one-third of the world’s terrestrial carbon reserves and play pivotal roles in the global carbon cycle. The net primary productivity (NPP) of grasslands serves as an essential indicator of the adaptability and responsiveness of a system to climate and soil change, offering valuable insights for improving the precision of global carbon cycle models. However, the mechanisms by which grassland ecosystems respond to environmental changes across different climate zones and humidity conditions remain complex and unclear, posing challenges for effective management and conservation of grasslands. In this study, a comprehensive dataset was constructed using the observed NPP data of grasslands worldwide, covering climate factors, such as temperature, radiation, and precipitation, as well as soil factors, such as soil water content, bulk density, and soil particle composition. Through regression analysis and the random forest algorithm, the responses of grassland NPP to environmental factors in different climatic zones are systematically discussed. Regression analysis helped to identify the quantitative effects of climate and soil factors on grassland NPP, whereas random forest algorithms revealed the relative importance and complex nonlinear relationships of each factor. In addition, an asymmetry index was used to analyze the response of grassland NPP to precipitation change, revealing the adaptability of grassland systems to precipitation variability under different climatic conditions and further improving the understanding of the grassland ecosystem response model. In arid regions, grassland NPP is primarily limited by water availability, with minimal influences from other climatic factors and soil properties. These findings provide valuable guidance for grassland management in arid areas, emphasizing the importance of water resource management for maintaining and boosting the productivity and resilience of grassland ecosystems in these regions. Conversely, the response of grassland NPP to environmental factors in humid climatic zones is complex. Grassland NPP was significantly influenced by energy factors such as solar radiation and temperature. Soil factors such as soil water content and bulk density also play crucial roles. This suggests that, under relatively adequate water conditions, grassland ecosystems in humid zones exhibit a more significant range of response mechanisms to environmental fluctuations. Grasslands in these areas must adapt not only to variations in climate factors but also to changes in soil conditions to maintain ecological balance and productivity. Therefore, grassland management in humid areas should adopt an integrated approach that considers the interaction between climate and soil conditions to enhance the resilience and sustainability of grassland systems. In terms of precipitation response asymmetry, this study revealed distinct response patterns for grassland NPP across different climate zones. In arid regions, grassland NPP exhibits a pronounced positive response to precipitation under conditions of high solar radiation, low vapor pressure deficit (VPD), and high soil sand content. This pattern indicates that grassland ecosystems in arid regions develop high efficiency in utilizing sporadic precipitation events, allowing for rapid increases in productivity under limited water input conditions. This phenomenon highlights the adaptability of grassland ecosystems in arid zones to effectively utilize short-term precipitation, thereby enhancing their survival capacity in response to the dual stresses of drought and high temperatures. Additionally, in humid climate zones, grassland NPP showed a more marked positive response to precipitation under moderate levels of precipitation and temperature as well as in soils with lower clay content. This finding reveals that, in humid regions, grassland productivity peaks under moderate precipitation levels, whereas excessive rainfall may lead to decreased soil aeration, thereby inhibiting root respiration and ultimately reducing productivity. This pattern indicates the need for appropriate management of soil moisture in humid areas to avoid the negative impacts of excessive precipitation and to maintain ecological health and grassland productivity. Finally, we identified a “threshold effect” on the response of grassland NPP to environmental factors. Grassland NPP demonstrated a positive response to changes in environmental variables up to a certain threshold, beyond which the response may weaken or even turn negative. This threshold effect was particularly pronounced under extreme climatic conditions, indicating the vulnerability of grassland ecosystems to such extremes. For example, in humid regions, when precipitation levels exceed an optimal threshold, a decline in soil aeration can lead to a reduction in the grassland NPP. These results suggest that management practices should focus on maintaining environmental variables within optimal thresholds for grassland ecosystems to enhance their resilience to climate extremes and preserve their productivity and stability. Future research could expand this study by examining the specific response mechanisms of different vegetation types, such as grasslands and shrublands, to climate change and by analyzing the long-term dynamic changes in ecosystems under shifting climate conditions. Exploring the role of microbial communities in grassland ecosystems, particularly their functions in carbon and nitrogen cycling, could offer a more comprehensive understanding of grassland diversity and stability. Incorporating remote sensing technology, ecological modeling, and artificial intelligence algorithms can further enhance the accuracy of predictive models for climate adaptation, laying the scientific foundation for tackling the complexities of future climate change. In conclusion, this study systematically uncovered the intricate mechanisms by which grassland ecosystems respond to climate and soil factors across diverse climate zones, by utilizing a comprehensive global dataset of grassland NPP. These findings provide essential data to enhance global carbon cycle models and lay a solid theoretical foundation for future grassland management and climate adaptation strategies. Beyond providing actionable recommendations for grassland management and ecological restoration, this study provides scientific insights crucial for maintaining grassland ecosystem resilience in the face of intensifying climate challenges. Finally, this study has far-reaching implications for understanding the global response of ecosystems to climate change, reinforcing the urgent need for informed and sustainable ecological practices.

Key words: grassland ecosystem, net primary productivity, spatial distribution, climatic factors, asymmetric response