Long-Term Flooding Mitigates the Linkage between Paddy Soil Organic Carbon Sink and Climate Factors

Understanding how artificial anaerobic environment (flooding) affects paddy soil ecosystem carbon (C) sequestrating has become imperative in the context of global climate change. However, the specific effects under various types of flooding management remain unclear. Here, we reported the results of 682 paired observations from 166 field experiments across typical rice-planting regions in China with a strong environmental gradient, with flooding effects on soil organic carbon (SOC) remaining relatively consistent. Accordingly, we employed nonmetric multidimensional scaling (NMDS) to categorize annual flooding periods into short (3–5 months) and long term (>5 months). The results showed that long-term flooding (48.52 Mg ha^–1) had a greater SOC sequestration capacity than short-term flooding (30.43 Mg ha^–1). Furthermore, the application of structural equation modeling (SEM) revealed that long-term flooding significantly mitigated the impacts of mean annual temperature (MAT) and mean annual precipitation (MAP), reducing them by a substantial 7.73-fold compared to short-term flooding. Briefly, longer submerged environments in long-term flooding mitigated the positive effects of MAT and negative effects of MAP, with the standardized total effects (STEs) of 10.7 and 6.2% (P < 0.05), respectively, which were much smaller than those under short-term flooding (21.3 and 67.8%, P < 0.05, respectively). Our findings highlight that an understanding of the relative contribution of anaerobic environment induced by artificially flooding to SOC in soil ecosystems is critical for guiding management efforts aimed at maintaining ecosystem SOC sequestration under global changes.