Soil organic carbon (SOC) primarily originates from plant inputs and the accumulation of microbial necromass. However, across the Qinghai-Tibet Plateau, a systematic and quantitative understanding of the accumulation patterns, relative contributions, and environmental driving mechanisms of these two carbon sources along elevational gradients has remained lacking.

To address the key scientific questions regarding the accumulation patterns and relative contributions of plant- and microbial-derived carbon as vital sources of SOC along elevational gradients, a research team from the Northwest Institute of Eco-Environment and Resources, Chinese Academy of Sciences (CAS), investigated both a local-scale vertical mountain transect and a regional-scale biogeographical transect on the Qinghai-Tibet Plateau. Utilizing lignin phenols and amino sugars as biomarkers for plant- and microbial-derived carbon, respectively, they quantitatively revealed the elevational distribution patterns and driving mechanisms of both carbon fractions across different spatial scales.

The findings showed that although the absolute contents of both plant- and microbial-derived carbon consistently increased with elevation, their relative contributions to the SOC pool exhibited contrasting trends. With rising elevation, the relative proportion of plant-derived carbon (lignin phenols) in SOC decreased significantly, whereas the relative proportion of microbial-derived carbon (amino sugars) increased substantially. The study revealed a shift in carbon source dominance regulated by critical elevation thresholds: below the critical threshold (2,415 m at the local scale and 3,650 m at the regional scale), SOC accumulation was predominantly driven by plant-derived carbon; conversely, once the elevation exceeded this threshold, microbial-derived carbon became the dominant contributor.

Analyses using random forest and piecewise structural equation modeling (piecewiseSEM) demonstrated that across both local and regional scales, soil total nitrogen, soil moisture (or aridity index), and soil pH were the core driving factors governing the accumulation of lignin phenols and amino sugars. The improvement in moisture conditions associated with increasing elevation not only directly or indirectly elevated plant-derived carbon inputs by promoting root biomass and soil total nitrogen accumulation, but also significantly fostered the accumulation of microbial-derived carbon by enhancing soil total nitrogen and microbial biomass carbon.

This study highlights the elevation-dependent divergent patterns and threshold effects governing the contributions of plant- and microbial-derived carbon to SOC on the Qinghai-Tibet Plateau, demonstrating that soil carbon sequestration in high-altitude ecosystems is primarily attributed to the accumulation of microbial-derived carbon. These insights provide valuable scientific guidance for improving the predictive accuracy of Earth system models regarding soil carbon dynamics under climate change.

The research has been published in the geosciences journal Global and Planetary Change under the title “Altitude-dependent divergent contributions of plant- and microbial-derived carbon to soil carbon on the Tibetan Plateau”. Xiaoming Mou from the Naiman Desertification Research Station of the Northwest Institute of Eco-Environment and Resources is the first author, and Associate Researcher Xuyang Wang is the corresponding author. This work was supported by the Youth Innovation Promotion Association of the Chinese Academy of Sciences, the Natural Science Foundation of Gansu Province, and the National Natural Science Foundation of China.

https://doi.org/10.1016/j.gloplacha.2026.105739