Soil organic carbon accumulation is mainly driven by soil nitrogen in rocky desertified mulberry plantation

Background and Aims Soil organic carbon (SOC), a critical determinant of soil functionality, remains inadequately characterized in its spatiotemporal dynamics and drivers within karst mulberry systems—an ecologically fragile region confronting severe rocky desertification. Methods This study elucidates SOC variability across typical karst landscapes through comparative analysis of mulberry plantations in rocky desertification zones (Rd) versus non-desertification areas (nRd) of central Guizhou, China, focusing on seasonal interactions with macro/micronutrients and biochemical factors. Results Key findings reveal: (1) Changes of SOC content in different soil types and seasons. SOC content in Rd plantations (31.51–39.71 g·kg ^− 1 ) consistently exceeded nRd counterparts (22.50–28.51 g·kg ^− 1 ) by 1.28–1.57-fold, with bimodal seasonal peaks in April/November and minima in May–July across both systems. (2) Carbon-nutrient coupling: SOC exhibited significant positive correlations with total nitrogen (TN), alkali-hydrolyzable nitrogen (AN), available potassium (AK), and glomalin-related soil proteins (T-GRSP: Total glomalin-related soil protein; EE-GRSP: Easily extractable glomalin-related soil protein)), contrasting with significant negative associations with available phosphorus (AP). (3) System-specific drivers: Nitrogen-limitation governed SOC dynamics dominantly. However, pH emerged as a key secondary regulator in nRd systems. In addition, soil type affected SOC accumulation by affecting Alkaline protease, T-GRSP and TN. Conclusion These findings establish nitrogen management as a critical lever for SOC sequestration optimization in karst mulberry systems while contextualizing landscape-specific edaphic controls. The work provides an empirical foundation for targeted carbon-smart practices in global karst agricultural ecosystems facing desertification pressures.