Changes of carbon stocks in alpine grassland soils from 2002 to 2011 on the Tibetan Plateau and their climatic causes

•SOC changes in alpine grasslands were estimated using repeated soil inventory.•Alpine meadows showed a markedly C gain, alpine steppes exhibited a slight C loss.•SOC changes were apparently related to the original SOC stocks in alpine steppes.•SOC changes were correlated with March-April precipitation in alpine meadows.•SOC changes were associated with MAP in alpine steppes.

Based on field observations, remote sensing, and modeling, recent studies have reported inconsistent changes in soil organic carbon (SOC) stocks in grasslands of the Tibetan Plateau over the past few decades. However, direct evidence about the changes in SOC stocks in the plateau's grasslands coming from in situ, site-by-site, repeated surveys is rare. In this study, we carried out a repeated soil sampling to assess the changes in SOC stocks in the alpine grasslands across the Tibetan Plateau. Across all 41 sites in the alpine grasslands, SOC stocks exhibited a significant increase from 2002 to 2011 at an overall rate of 4.66 g C m− 2 yr− 1. Mesic and low-temperature-limited alpine meadows showed an average carbon gain of 25.8 g C m− 2 yr− 1, whereas the relatively dry alpine steppes exhibited a slight carbon loss of 11.9 g C m− 2 yr− 1. Spatially, the changes in SOC stocks were significantly related to the original SOC stocks across alpine steppes, and soils with low carbon tended to gain carbon. Moreover, the changes in SOC stocks were also associated with March-April precipitation in alpine meadows, and with mean annual precipitation (MAP) in alpine steppes, with drier sites generally gaining carbon. Overall, the alpine grasslands of the Tibetan Plateau significantly accumulated SOC over this 10-year period, but many more site surveys are needed to comprehensively access the changes in SOC stocks across alpine grasslands on the plateau; and management strategies enhancing the ability of C sequestration should differ between alpine meadows and steppes due to their contrasting climate conditions.