Clarifying the spatial distribution of soil organic carbon (SOC) can provide a theoretical basis for mitigating carbon emissions. The characteristics of SOC and soil organic carbon density (SOCD) change in different vegetation and soil types, and the response mechanism of SOC content to environmental factors are unclear. Thus, 131 sites were selected for sampling from the 0‒30 cm soil layer to study regional SOC and SOCD spatial distribution. The results showed that the SOCD in the northwestern region was lower than that in the southeastern in the northeast of the Qinghai-Tibet Plateaue. Both SOC and SOCD were affected by the vegetation type. The order of vegetation types was swamp > meadow > steppe > desert. Furthermore, SOC content decreased with increasing soil depth in the 0‒30 cm soil layer. The SOC and SOCD contents also differed among the different soil types. The order of SOC from largest to smallest was alpine meadow soil > bog soil > chestnut soil > saline-alkali soil > alpine steppe soil > grey-brown desert. The path analysis showed that TN significantly positively affected SOC (P < 0.001). This study aimed to provide a scientific basis for grassland carbon sink management in the Qinghai-Tibet Plateau.

Understanding the characteristics of long-term changes in the water use efficiency (WUE) of grassland ecosystems is vital for WUE improvement on the Qinghai-Tibet Plateau. In this study, five vegetation types, namely alpine shrub, desert, grassland, meadow, and swamp, were evaluated. The changes in WUE over the past 16 years were calculated using the total primary productivity and latent heat flux data of the ecosystem from 2006 to 2021. In addition, meteorological data were used to further explore the relationship between WUE and environmental factors. The WUE of alpine desert, meadow, and swamp showed an increasing trend. In contrast, alpine shrub and grassland WUE showed a decreasing trend, with the WUE of shrub being significantly higher than that of grassland on the interannual scale. The WUE of all vegetation types showed seasonal maximum and minimum values in July and January, respectively, and the WUE of shrubs was significantly higher than that of the other vegetation types. The structural equation model showed that precipitation, temperature, and relative humidity were the main positive influences on the WUE of grasslands on the Qinghai-Tibet Plateau, whereas net radiation had a negative influence. Climate factors may substantially impact future changes in the WUE of various ecosystems. The results of this study provide a theoretical basis for further study of WUE changes in the grasslands of the Qinghai-Tibet Plateau.