Interannual variation in precipitation predominantly controls mineral-associated organic carbon dynamics in a Tibetan alpine meadow

Abstract

Soils in alpine ecosystems store a large amount of organic carbon (C) with a significant portion sorbed to reactive soil minerals. However, impacts of ongoing global change factors on mineral-associated organic C dynamics are highly uncertain in alpine regions. Utilizing a multi-factor simulation experiment in a Tibetan alpine meadow since May 2015, we examined the effects of air warming, nitrogen input and precipitation changes on calcium (Ca)- and iron (Fe)-associated C dynamics in 2019–2020. We found no significant difference in Ca- or Fe-associated C concentrations among treatments. However, both Ca- and Fe-associated C concentrations were significantly higher in 2020 with abnormally high rainfall (+40%) than in 2019 with normal rainfall. High rainfall significantly increased soil moisture, reduced soil aggregation and released soil dissolved organic C. High soil moisture promoted the formation of both Ca- and Fe-associated C, likely through facilitating Ca-binding to clay surface as a bridge for mineral-C complexes or through increasing solubility of Fe oxides. In contrast, a low degree of water addition (<30%) immediately following each rainfall event in field did not significantly affect either Ca- or Fe-associated C. Taken together, our results provide new insights into the potential mechanisms through which interannual precipitation variability controls mineral-associated C persistence in alpine meadow ecosystems, suggesting that the pattern of rainfall change may dominate its impact on dynamics of organic C retained by reactive minerals.