Different impacts of artificial thicketization of Caragana korshinskii and Hippophae rhamnoides on soil organic carbon in alpine grasslands of the Qinghai–Tibetan Plateau

Grassland shrub encroachment is known to change soil organic carbon (SOC) storage, but the effect of artificial thicketization on SOC in alpine grasslands of the Qinghai–Tibetan Plateau remains unclear. In this study, we investigated the effects of two common shrubs, leguminous Caragana korshinskii and non‐leguminous Hippophae rhamnoides, on SOC at a reforestation site on the Qinghai–Tibetan Plateau. While C. korshinskii had no significant effect on SOC content, H. rhamnoides significantly increased SOC content. In both shrub communities, there was a significant positive correlation between SOC content and the coverage, plant aboveground biomass, dominant plant species biomass, total and available nitrogen, total phosphorus, and proportion of water‐stable aggregate of greater than 250 μm. Structural equation modeling showed that the common path by which the two shrub communities affected SOC was that the dominant species affected soil structure and the available nitrogen content by influencing community biomass, which had indirect effects on SOC. Additionally, C. korshinskii participated in the regulation of SOC. This result provides an important empirical reference and key insights into the carbon cycling mechanisms of reforested grasslands on the Qinghai–Tibetan Plateau.