Warming-induced greenhouse gas fluxes from global croplands modified by agricultural practices: A meta-analysis

Climate warming increases the emissions of soil greenhouse gases (GHGs) by stimulating carbon (C) and nitrogen (N) processes in terrestrial ecosystems, contributing to climate change. However, the responses of soil GHG fluxes to warming from global agricultural ecosystems remain unknown. Here, we evaluate the effects of warming on soil GHG fluxes from global croplands under different agro-ecosystems, cropping systems, crop species, and N fertilizer levels, and determine the potential mechanisms through a meta-analysis of field observations. The results showed that warming (+2.0 degrees C on average) significantly enhanced soil carbon dioxide (CO2) emissions (i.e., soil respiration) by 14.7% and nitrous oxide (N2O) fluxes by 12.6% across croplands and increased soil methane (CH4) uptake by 21.8% in uplands and CH4 release by 23.4% in paddy fields. The responses of C gas fluxes to warming were regulated by initial C substrates, initial wetness, and changes in temperature in croplands. The responses of N2O fluxes to warming were mainly associated with changed NH4+-N and NO3--N as well as initial wetness and N fertilizer in croplands. The responses of soil GHG fluxes to warming were generally comparable among different crop species and N fertilizer levels, respectively. However, the responses of CO2 emissions and CH4 release to warming were significantly higher in upland-paddy fields than in uplands and paddy fields; the warming-induced changes in CH4 release was significantly greater in rotation cropping systems than in single- and double-cropping systems. This synthesis highlights the important role of climate warming in increasing soil GHG fluxes from croplands, underscoring the critical need for agricultural practice adjustment to mitigate climate change in the future.