The impact of extreme climate on soil organic carbon in China

• This study quantifies impacts of 19 extreme climate indices on China’s SOC changes. • Topography dominates SOC changes under extreme climate conditions. • Extreme heat and dry reduce SOC, with sharp losses in North China. • Extreme cold and wet boost SOC in Northeast but weakly in humid regions. • Forests and grasslands show highest SOC sensitivity to extreme climate. Quantitative studies on the national-scale effects of extreme climatic events on soil organic carbon (SOC) remain scarce, thus limiting our understanding of SOC dynamics. This study utilized 4515 publicly available soil samples to quantify the impacts of 19 extreme climatic indices (ECIs) on ΔSOC reservoirs in China through a hybrid space-for-time and meta-analysis approach. Overall, 16/19 ECIs were negatively correlated with ΔSOC, with the minimum temperature of the coldest night (TNn) showing the strongest negative correlation. Notably, topographic factors played a pivotal role in the modeling process, contributing an average of 25 %, followed by ECIs. Under the influence of the ECIs, SOC exhibited spatial variation. Extreme heat resulted in the greatest SOC losses in cold regions, such as North China, with average reductions of > 5 %, whereas its impact was weaker in South China, with SOC losses of ∼3 %. Extreme cold and wet indices promoted SOC accumulation in the Northeast China, with increases of ∼3 %, but showed a weaker response in the humid region, where the SOC increased by only 1 %. At the national scale, the impacts of extreme climatic events on SOC in the 0–20 cm ranged from −2.36 Pg to 2.34 Pg. Different ecosystems responded variably, with forest and grassland ecosystems being more sensitive to ECIs, potentially due to higher organic matter inputs and greater ecosystem complexity. In contrast, bare land exhibited weaker responses due to limited vegetation cover and organic inputs. These findings provide valuable insights into SOC dynamics at national scale during extreme climatic events.