Soil inorganic carbon stock and its changes across the Tibetan Plateau during the 1980s–2020s

Soil carbon is an important component of the global carbon cycle and consists of organic carbon (SOC) and inorganic carbon (SIC) pools. Although SIC has been recognized as a large pool, little is known about how it has been influenced by climate change and land degradation on a decadal timescale. Here, we evaluated the magnitude of the SIC stock and detected its changes under different land cover types across the Tibetan Plateau over the past decades based on repeated SIC measurements in the 1980s and 2020s at the same sites. In the soils of the Tibetan Plateau, SIC accounts for 45% and 49% of the total (organic plus inorganic) soil carbon at depths of 0–50 cm and 0–100 cm, with estimated SIC stocks of approximately 15.6 and 20.9 Pg C, and average SIC densities of 7.2 and 9.4 kg C m−2, respectively. Partial correlation and variation partitioning analyses revealed that the spatial distribution of SIC was predominantly influenced by soil properties (soil type, texture, and pH) and climate, explaining 12.1% and 7.5% of the SIC variance, respectively. Between the 1980s and the 2020s, an overall accumulation of SIC was observed for all land cover types, with an average increase of 2.3 and 2.0 g C kg−1 for the topsoil (notably 0–20 cm) and subsoil (notably 20–50 cm), respectively. However, the response of SIC to a changing climate is more nuanced; increased precipitation may reduce SIC stock in arid areas by enhancing leaching, whereas warming temperatures may contribute to SIC accumulation in humid regions. Overall, these findings have important implications for understanding the role of SIC in the global carbon cycle under future climate change events.