Climate and soil shape vertical carbon sequestration patterns in high-altitude grasslands of the Qinghai–Xizang plateau

The alpine grasslands of the Qinghai–Xizang plateau (QXP) serve as significant carbon reservoirs, storing approximately 2.5% of global soil organic carbon (SOC). However, the mechanisms governing SOC distribution across different environmental gradients remain insufficiently understood. In this study, we quantified SOC and its labile fractions (DTC, DOC, MBC) across four major grassland types—Alpine meadow (AM), alpine swamp meadow (ASM), alpine steppe (AS), and alpine desert steppe (ADS)—Using 120 soil profiles (0–60 cm) sampled along a 1200 km transect. Our results revealed significant vertical stratification of SOC, with the highest concentrations found in the topsoil (0–10 cm). Alpine meadows (AM) and alpine swamp meadows (ASM) exhibited higher SOC and MBC levels than alpine steppes (AS) and alpine desert steppes (ADS). Soil physicochemical properties, particularly moisture content and underground biomass, were the primary drivers of SOC dynamics, while climate factors, especially temperature and precipitation, negatively influenced labile carbon pools (DTC, DOC). The study also showed that microbial indicators, such as MBC, remained stable in certain ecosystems, suggesting ongoing microbial activity and strong carbon‑nitrogen coupling. These findings emphasize the critical role of soil properties in regulating carbon sequestration in high-altitude ecosystems and underscore the vulnerability of carbon stocks to climate change. This research provides new insights into the mechanisms driving soil carbon dynamics in alpine regions, offering important implications for refining carbon cycle models and improving future climate projections