Rise in wetland carbon uptake linked to increased potential evapotranspiration

Abstract

Precisely assessing wetland net ecosystem productivity (NEP) is important for accurately evaluating global carbon budgets. However, constrained by the quality of observational data and insufficient understanding of driving mechanisms, assessments of China's wetland NEP still have considerable uncertainties. Therefore, this study assessed continuous observations from 30 eddy covariance flux towers across various wetland types in China and applied the random forest (RF) model to simulate the spatiotemporal dynamics of China's wetland NEP. The results showed that from 1982 to 2020, China's wetlands represented a net C-CO₂ sink overall, with an average NEP of 21.61 ± 0.04 mg C m⁻² h⁻¹ and annual net C-CO₂ absorption of 56.23 Tg C. Riverine and coastal wetlands had the highest NEP, while freshwater marshes had the lowest. From 1982 to 2020, the wetland NEP in China exhibited a significant increasing trend. Further analysis indicated that potential evapotranspiration (PET) is the main driving factor behind the significant increase in NEP in China's wetlands, with a clear threshold effect: NEP rises with PET up to a certain point (e.g., 160 mm), after which it declines. This study accurately quantified the spatiotemporal dynamics of China's wetland NEP and revealed the critical impact of PET on NEP, thus providing a new perspective for performing wetland carbon cycle research and formulating climate change mitigation strategies.