Comment on bg-2022-171

Abstract

Sandy land is an important part of terrestrial ecosystem, which has a substantial impact on maintaining global ecological health and security. However, there is still a scarcity representative studies of climate change’s effect on the carbon fluxes (NEE: net ecosystem CO2 exchange; Reco: ecosystem respiration; GPP: gross primary productivity). Eddy covariance technique was used to determine carbon fluxes and climatic conditions in this ecosystem from 2017 to 2021. At an annual scale, the semi-fixed sandy land was found to be a net carbon release, the value of annual average NEE was 6.81 ± 36.35 g C m-2 yr-1. It functioned as a carbon source in dry years (2017 and 2020), but was a carbon sink in wet years (2019 and 2021) and a normal year (2018). At seasonal scale, according to the Random Forest, deep soil water content (SWC80) and photosynthetic photon flux density had a great impact on NEE and GPP, whereas shallow and deep soil water (SWC10 and SWC80) dominated Reco. At a monthly scale, the multiple stepwise regression showed that soil temperature, precipitation (PPT) and SWC were the dominant environmental factors. At an annual scale, correlation analysis showed that total annual PPT was negatively correlated with NEE. Our results illustrate the importance of climate variations for the NEE, Reco, and GPP at different time scales in arid and semi-arid areas. They also highlight the importance of water availability (the pattern and intensity of PPT and SWC at different depths) on regional and global carbon cycles.