Microbial Nutrient Acquisition and Modelled Carbon Use Efficiency Along Two Grassland Elevation Sequences

Soil microorganisms play an important role in regulating carbon and nutrient cycling in mountain grasslands. However, whether microbial nutrient limitation and carbon use efficiency (CUE) follow similar elevation patterns across plant communities remains unclear. To this end, we measured soil physicochemical properties, microbial biomass and extracellular enzyme activities in Sophora alopecuroides-dominated (SC) and grass-dominated (GC) communities in the Tuhulasu grassland, Xinjiang, each sampled at three elevation bands, and calculated CUE using a stoichiometric model. Results showed that soil organic carbon increased along both sequences, while microbial biomass and enzyme activities showed element-specific patterns. Mean vector length peaked at 1500 m in both communities, whereas mean vector angle peaked at 1300 m in SC and 1800 m in GC, indicating the highest relative P-acquisition signal within each sampled elevation sequence. Total-pool CUE declined across both sequences; extract-based CUE declined in SC but varied little among GC means. Soil properties were associated with these indicators in the overall RDA. This study revealed that relative C- and P-acquisition signals peaked at different elevations, while modelled CUE patterns varied between the sampled elevation sequences and resource inputs. Vegetation context and resource-pool definition should therefore be considered when interpreting nutrient-acquisition indicators and modelled CUE for soil monitoring that informs sustainable grassland management.