Soil moisture and nitrogen control particulate and mineral-associated organic carbon on the Qinghai-Tibet Plateau

Soil organic carbon (SOC) fractions are important input parameters for process-based models, while the distribution and influencing factors of SOC fractions in alpine permafrost regions remain largely unknown. Here we collected 150 soil samples from 50 sites for surface 30 cm depth in permafrost regions on the Qinghai-Tibet Plateau (QTP).

We analyzed SOC content, particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), and further investigated their relationship with environmental factors using regression and random forest models.

The results showed that the POC/SOC ratios were significantly lower in alpine steppe (5%—12%) than in meadows (28%—49%) and wet meadows (34%—47%). Pedotransfer functions and random forest models showed that total nitrogen and soil moisture were the most important factors affecting POC content, while total N, soil moisture and below ground biomass were the main factors influencing MAOC content.

Our results provide a clear distribution pattern of soil organic matter fractions under different land cover types, and thus serve as a scientific basis for parameterization of carbon pools for process-based models.