Potential evapotranspiration determines changes in the carbon sequestration capacity of forest and grass ecosystems in Xinjiang, Northwest China

Abstract

Accurately understanding carbon stock in forest and grass ecosystems, determining carbon sequestration capacity (CSC), and identifying influencing factors over time are crucial for regional carbon budget assessment. This paper studied changes in gross primary productivity (GPP), net primary productivity (NPP), and net ecosystem productivity (NEP) of forest and grass in Xinjiang, China from 1990 to 2020, showing the evolution of CSC and identifying key factors. The results showed that the photosynthetic carbon sequestration capacity of forest-grass ecosystems increased significantly over 30 years, with a growth rate of 2.57 g C m−2 a−1. Total carbon sequestration capacity also showed an increasing trend, with NPP increasing from 7.42 g C m−2 per decade in the 1990 s to 34.91 g C m−2 per decade in 2010–2020. Net carbon sequestration capacity was also effectively increased, with NEP increasing from − 45.98 g C m−2 to 30.20 g C m−2 from 1990 to 2020, a clear shift from a carbon source to a sink. CSC is higher in mountainous areas and areas around rivers, and stronger in the northern regions. Forests are the most important carbon reservoir, with an annual net carbon stock of 0.18 million tonnes, and grasslands have a high carbon sequestration potential, with an annual photosynthetic carbon stock of 154 million tonnes. The ecological water transfer projects implemented in the Tarim River Basin have helped to increase the CSC. Potential evapotranspiration (PET) greatly affects carbon use efficiency, explaining 59.05% of it. The interaction of any selected factors with PET enhances the explanatory power. The study results offer scientific and theoretical backing for attaining regional carbon neutrality.