Patterns of soil organic carbon accumulation and microbiological mechanisms in mountain ecosystems

Plant- and microbial-derived compounds has been recognized as key contributors to vulnerable and stable soil organic carbon (SOC) pools. However, the relative contributions of these sources along altitudinal gradients remain unclear. This study quantified the contributions of plant- and microbial-derived carbon (C) to SOC across four distinct vegetation zones along an altitudinal gradient ranging from 2600 to 3670 m in northwest China. SOC content increased significantly along altitudinal gradients in the 0–20 cm and 20–40 cm, indicating greater C sequestration in higher elevations. Both plant lignin and microbial necromass also increased with altitude in both soil layers. Notably, in lower altitudes, SOC accumulation was predominantly driven by plant-derived C, while in higher altitudes, microbial-derived C was dominated. The substantial SOC storage in higher altitudes is more microbially processed, which contributes to greater SOC stability, as opposed to the lower altitudes, where SOC is less stable and more vulnerable to environmental change. Regression analysis and random forest modeling reveal that soil pH, moisture, and total nitrogen as the primary regulators of plant lignin and microbial necromass, surpassing the influence of plant inputs such as root biomass. In conclusion, the content of both plant lignin and microbial necromass increases with altitude, while their respective contributions to SOC follow divergent patterns. These findings have significant implications for predicting C loss as a result of global climate change, underscoring the need for targeted conservation strategies across different altitudinal zones.