Agricultural Water Management (Sep 2023)
Spatiotemporal variations of cropland carbon sequestration and water loss across China
Abstract
Croplands play a critical role in regulating terrestrial water and carbon cycles and provide essential social services for humans. Investigating the characteristics of water and carbon flux in cropland ecosystems offers valuable information for advancing sustainable agriculture management. Combining the up-to-date Moderate Resolution Imaging Spectroradiometer and cropland distribution data, this study quantified the temporal-spatial variations of evapotranspiration (ET), gross primary productivity (GPP), and ecosystem-scale water use efficiency (WUE) in paddy (PF) and non-paddy field (NPF) over China from 2000 to 2021. The results showed that annual ET in both PF and NPF presented an increasing trend from northwest to southeast of China, with mean annual ET totaling 625 ± 43 mm yr−1 and 487 ± 45 mm yr−1 in PF and NPF, respectively. The Sen’s slope showed that annual ET presented significantly increasing trends (p < 0.01), with a rate of 66.7−12.2+10.9 mm yr−1 decade−1 in NPF and 59.8−14.9+16.6 mm yr−1 decade−1 in PF. The magnitudes of the increase in annual ET mainly came from the ET increase in summer, with the quantified contribution rates of 38.4 % in PF and 50.74 % in NPF. The spatial variations of cropland annual GPP agreed well with that of annual ET. The mean annual GPP in PF and NPF was estimated at 1029 ± 57 gC m−2 yr−1 and 776 ± 67 gC m−2 yr−1 from 2000 to 2021, respectively, along with its significantly increasing trend at 84.0−14.2+15.9 gC m−2 decade−1 and 96.3−9.7+14.2 gC m−2 decade−1 (p < 0.01) in PF and NPF during this period, respectively. The increase in spring GPP mainly contributed to the increasing annual GPP in PF. In contrast, the rising GPP in spring and summer primarily resulted in the increasing annual GPP in NPF. The mean annual WUE is 1.65 ± 0.05 gC m−2 kg−1H2O in PF and 1.59 ± 0.03 gC m−2 kg−1H2O in NPF, respectively. The investigations of the variations of WUE demonstrated that both PF and NPF experienced negative trends in China, but the trends were not uniform, and disparities existed across the sub-agricultural districts. The quantified spatial and temporal patterns of how croplands trade water for carbon will help better manage agricultural water resources and ensure food security.
