Abstract: Exploring soil organic carbon (SOC) changes along environmental gradients in climate transition zone is essential for predicting soil organic carbon dynamics under climate change. To understand the spatial variations of SOC content and storage in the transition zone of subtropical to warm-temperate climate, 15 monitoring forest plots were set up in Lishan National Nature Reserve in Shanxi Province along an elevation gradient from 890 m to 2200 m above sea level at a 100 m interval. We assessed the elevational changes in SOC content and storage and their relationships with plant diversity, soil physicochemical and climatic factors, and microbial characteristics by using five-point sampling method. The results showed that both SOC content and storage showed overall U-shaped trends along the elevational gradient. The SOC content and storage peaked at 1645 m (75.41±14.05 g·kg^-1) and 894 m (51.85±9.89 Mg·hm^-2), respectively. Results of the Mantel test showed that SOC content was significantly correlated with soil factors, climatic factors, and microbial species richness, while the spatial variation in SOC storage was only significantly correlated with soil factors and microbial species richness. Environmental factors explained 64.7% and 33.9% of the total variations of elevational patterns in soil SOC content and storage, respectively. Annual precipitation was the largest predictor (14.8% of total explained variance) for SOC content, followed by NO₃^--N (13.4%) and  annual mean temperature (13.2%). For SOC storage, soil total phosphorus had the strongest effect with over 15% of total explained variance, followed by NO₃^--N (8.7%) and  annual mean temperature (7.5%). This study provides an important reference for evaluating soil organic carbon storage and its variation in forests in the climatic transition zone.

Key words: warm-temperate forest, soil organic carbon, elevational gradient, carbon storage, soil bacteria, soil fungi