Multiscale drivers and tipping points regulating particulate and mineral-associated organic carbon across Central Asian grasslands

Drylands constitute more than 40 % of Earth’s land surface and play a vital role in the global carbon cycle. However, the responses of key soil organic carbon fractions, specifically mineral-associated organic carbon (MAOC) and particulate organic carbon (POC), to environmental changes in arid grasslands remain poorly understood, limiting reliable climate projections and effective carbon management. Here, we integrated systematic sampling conducted at 355 sites across grasslands in Central Asia (e.g., Xinjiang, Kazakhstan, Tajikistan, and Kyrgyzstan) with interpretable machine learning model to quantify the drivers along environmental gradients and tipping points regulating MAOC and POC. Our results revealed that both MAOC and POC decreased with increasing temperature, with MAOC exhibiting greater sensitivity in the subsurface layer. Net primary productivity (NPP) was the primary driver of MAOC and POC, but via distinct pathways, POC accumulation reflects the direct input of plant residues, whereas MAOC formation depends on microbial transformation and mineral stabilization and is influenced by broader climatic and edaphic gradients. Tipping point analyses revealed distinct nonlinear response patterns. For POC, accumulation was enhanced only when NPP exceeded 0.41 in both soil layers, and bulk density promoted POC storage below 1.06 g cm−3 in surface soil and 1.08 g cm−3 in subsurface soil. For MAOC, accumulation increased only when NPP exceeded 0.36 in the surface layer and 0.51 in the subsurface layer, whereas it was suppressed when soil pH increased above 6.70 and 7.45, respectively. Our study provides the first quantitative analysis of environmental drivers and tipping points for POC and MAOC in grasslands of Central Asia across multidimensional environmental gradients. These insights highlight that soil carbon management in drylands should consider distinct stabilization mechanisms: in low-clay and drier soils, strategies may focus on enhancing MAOC persistence through regulating soil chemical environments and mineral availability, whereas in relatively wetter areas, promoting plant productivity is likely more effective for sustaining POC sequestration.