Characteristics and influencing factors of carbon source/sink variations in the Zoige grassland wetland ecological function zone on the eastern slope of the Tibetan Plateau

Net ecosystem productivity (NEP) refers to the portion of net primary productivity (NPP) that is available for carbon cycling in terrestrial ecosystems after subtracting photosynthetic carbon consumed by heterotrophic respiration. The amount of the NEP reflects the size of carbon sinks/sources in terrestrial ecosystems, holding great significance for the research of climate change and global carbon cycle. In this study, the NEP of the Zoige grassland wetland ecological function zone (ZGW) on the eastern slope of the Tibetan Plateau from 2001 to 2020 is estimated by using the improved Carnegie-Ames-Stanford Approach model for NPP and a statistical model for soil heterotrophic respiration, based on the meteorological data, vegetation data and socioeconomic data. Additionally, the spatio-temporal variations of the NEP are analyzed, and the influences of natural factors and anthropogenic activities on the NEP are investigated. The results indicate that the ZGW overall plays a role as a carbon sink, and the carbon sink area accounts for approximately 99.3% of the whole ZGW. The annual average NEP in the study area is 447.9 g·m⁻², showing a gradual increase at a rate of 5.0 g·m⁻²·a⁻¹, although the increasing trend is not significant. The carbon sink capacity increased in 93.5% of the ZGW, remained relatively stable in 5.9% of the ZGW, and decreased and significantly decreased in 0.6% of the ZGW. Climate warming and humidifying promote the enhancement of carbon sink capacity in the ecosystem of the ZGW, and precipitation is the dominant climatic factor influencing NEP variations. Natural factors are the determinants of NEP variations, while anthropogenic activities play a secondary role. The implementation of ecological restoration and management projects in the areas along the Yellow River, around the main roads and the core area of wetlands, as well as the continuation of green and coordinated development policies of orderly developing grassland resources, is conducive to enhancing vegetation carbon sink capacity of the ZGW.