Nitrogen Drains a Dry Grassland's Mineral Carbon Only When the Soil Is Warmed

Nitrogen added to a semi-arid grassland left the carbon stored in its soil minerals alone, and the same nitrogen on warmed plots increased the loss of that carbon by about 9.1%. Tongshuo Bai of Nanjing Agricultural University and colleagues reported the field result Oct. 19, 2026.

Dryland soils hold carbon in two forms: organic carbon in plant and microbial remains, and inorganic carbon in minerals such as carbonate. The authors write that the inorganic pool's response to global environmental change has been largely overlooked, and that forecasts of dryland carbon need to account for how vulnerable it is. Their paper appears in Nature Geoscience.

Bai; the senior author, Shuijin Hu of Nanjing Agricultural University and North Carolina State University; and their co-authors ran an 8-year field manipulation experiment in a semi-arid grassland and paired it with a meta-analysis of 44 observations. The experiment tested warming, reactive nitrogen input and altered precipitation. Wetter or drier conditions had no effect on soil inorganic carbon. Nitrogen on its own had none either. The two drivers reached the pool only in combination.

The loss arrived together with faster microbial processing of soil nitrogen, including nitrification, the step in which microbes turn ammonium into nitrate and release acid. From that, the authors suggest the added acid is what governs whether the soil's carbonate dissolves or stays in place.

Both the field experiment and the meta-analysis found nitrogen, warming or the two together moving soil inorganic and organic carbon in opposite directions, which the authors read as a trade-off between the two pools.

The data and the code behind the analysis are posted publicly on Zenodo.