Stoichiometric shifts in surface soils over broad geographical scales: evidence from C hina's grasslands

Aim The identification of stoichiometric flexibility is crucial for understanding carbon–nitrogen–phosphorus (C–N–P) interactions and ecosystem dynamics under a changing environment. However, current evidence of stoichiometric flexibility mainly comes from manipulation experiments, with little evidence from large‐scale observations. Location Alpine and temperate grasslands across northernChina. Methods Using soil profiles derived from a historical national soil inventory and a contemporary regional soil survey acrossChina's grasslands, we examined temporal changes in topsoilC:N:Pratios over recent decades. Results TopsoilC:Nratios of five major grassland types exhibited some flexibility but did not show significant changes over the sampling interval. Non‐significant changes in topsoilC:Nratios were observed both in alpine grasslands on theTibetanPlateau and in temperate grasslands on the Inner Mongolian Plateau. Consistent with the relatively stableC:Nratios, the slope of the soilC–Nstoichiometric relationship did not differ significantly between the two sampling periods. SoilN:Pratios in the surface layer increased significantly over the sampling interval, however, with an overall increase of 0.60 (95% confidence interval 0.58–0.62). A larger increase in soilN:Pratio was found in temperate grasslands on theInnerMongolianPlateau than in alpine grasslands on theTibetanPlateau. Moreover, the slope of the soilN–Pstoichiometric relationship in these grassland ecosystems became steeper over the sampling interval. Main conclusions These results demonstrate the stability of topsoilC:Nstoichiometry but variability inN:Pstoichiometry over broad geographical scales, highlighting that soilCandNare tightly coupled, butNandPtend to be decoupled under a changing environment.