Trade-offs between soil inorganic and organic carbon driven by multiple global environmental changes

Dryland ecosystems store large amounts of both soil organic and inorganic carbon, yet the responses of soil inorganic carbon to global environmental change remain largely overlooked despite the potential vulnerability of this carbon pool. Here we aim to determine how soil inorganic and organic carbon respond to multiple global change drivers (warming, reactive nitrogen input and altered precipitation) using an 8-year field manipulation experiment in a semi-arid grassland and a meta-analysis based on 44 observations. We found that altered precipitation has no effect on soil inorganic carbon, but warming and nitrogen input interactively affect it. Specifically, nitrogen input alone does not affect soil inorganic carbon, but it increases soil inorganic carbon loss (~9.1%) when combined with climate warming. This inorganic carbon loss co-occurs with enhanced microbial nitrogen mineralization and nitrification, suggesting that enhancement of proton production due to nitrification controls soil inorganic carbon dissolution and persistence. Furthermore, both the field study and meta-analysis show that nitrogen input and/or warming induce contrasting changes in soil inorganic and organic carbon, suggesting a trade-off between soil inorganic and organic carbon under these two major global change drivers. These results highlight the need to account for the vulnerability of soil inorganic carbon when predicting dryland carbon dynamics under future climate change scenarios.