Dynamic variations in grassland ANPP and its response to climatic factors in the Qilian Mountains from 2000 to 2020

Estimating potential aboveground net primary productivity (ANPP) is essential for providing a decision-making basis for the adaptive management of grasslands. Based on climate, soil, and vegetation data, in conjunction with the CENTURY model and factor analysis, we examined dynamic variations in the ANPP of grasslands and their correlation with climatic factors in the Qilian Mountains from 2000 to 2020. The results showed that optimum and maximum temperatures for plant growth were sensitive parameters of the CENTURY model. Responses of ANPP to the two temperatures were opposite. Simulated ANPP using the CENTURY model was in good agreement with measured ANPP, with correlation coefficients of 0.87, 0.82, 0.77, 0.66, and 0.73 in alpine meadows, alpine steppes, alpine deserts, temperate steppes, and temperate deserts, respectively. These results suggested that the CENTURY model was applicable in simulating grassland ANPP. During the study period, ANPP of all grassland types exhibited an overall increasing trend. Alpine meadow ANPP showed the highest increase among grassland types, and the increasing trend was significant, at a rate of 12.1 g C·m⁻² (10a⁻¹). Moreover, annual mean air temperature and precipitation showed a significant increase, while there was a notable decline in annual solar radiation. ANPP was positively correlated with annual mean air temperature and precipitation but negatively correlated with annual solar radiation. In addition, the correlation between ANPP and air temperature was slightly higher than between precipitation and solar radiation. The above results have confirmed that a warming and humidification climate may increase grassland ANPP in the Qilian Mountains over the past two decades. It was also found that an increasing rate of ANPP varied among grassland types. Therefore, it is important to consider favorable climatic conditions and utilize the size and variation of ANPP as a guide for grassland protection and restoration to build an ecological barrier for the Qilian Mountains.