Soil inorganic carbon stocks increase non-synergistically with soil organic carbon after ecological restoration practices in drylands

Ecological restoration practices have been widely adopted to increase soil carbon stocks by improving soil organic carbon (SOC). However, the effects of these practices on the other important soil carbon component, soil inorganic carbon (SIC), remain unclear. To address this, a meta-analysis based on 45 publications and 37 sites was conducted to quantitatively assess the dynamic changes in SIC stocks due to typical restoration practices, including conversion of cropland to forest (C-F), cropland to grassland (C-G), desert to cropland (D-C), conservation agriculture (CA), and desert to forest (D-F). Results showed that, among the restoration practices increasing the SOC stocks, the SIC stocks decreased after the C-F (-34.7%) and C-G (-15.8%) conversions and CA (-6.8%), but increased after the conversion of D-C (2.6%) and D-F (46.9%). Additionally, in terms of recovery duration, the negative effect of C-G on SIC stocks may vanish with increased recovery duration, whereas SIC stocks showed a prominent increase initially after CA and then decreased over time; the response to D-F conversion of SIC stocks remained consistently positive over time. Furthermore, the non-synergistic changes with SIC and SOC could be due to variations in edaphic factors, while the effects edaphic factors on SIC stocks were different under various ecological restoration practices. Among all the impact factors, mean annual temperature, initial SIC stocks, and types of ecological restoration practice, were the most crucial factors explaining the variation in SIC stocks with ecological restoration. Collectively, the results highlight that the change in SIC stocks is asynchronous with the increase in SOC stocks in space and time after ecological restoration, further indicating that changes in SIC stocks should be paid more attention when assessing and predicting carbon sequestration following various ecological restoration practices.