Abstract: Plant elemental composition and stoichiometry, central to ecological function, are strongly influenced by global change drivers like nitrogen (N) deposition and land-use practices such as mowing. However, a holistic understanding of how multi-elemental composition (i.e., biogeochemical niches) mediate species-specific responses to these drivers remains limited. We conducted a decade-long field experiment in a meadow steppe, subjecting two dominant species, Leymus chinensis (a grass) and Carex duriuscula (a sedge), to N addition and mowing treatment. We quantified foliar concentrations of nine elements (K, Ca, Na, Mg, Al, Fe, Mn, Cu, Zn) to characterize their biogeochemical niches and stoichiometric homeostasis. Our results revealed that the resource-conservative L. chinensis maintained high stoichiometric homeostasis and a stable biogeochemical niche size and hypervolume under N addition, correlating with increased biomass. In contrast, the resource acquisitive species C. duriuscula showed greater plasticity, and mowing induced a significant change in its foliar element biogeochemical niche size and hypervolume, which were positively correlated with its biomass. Random forest analysis identified biogeochemical niche characteristics as a key driver of biomass for C. duriuscula but not for L. chinensis, where N addition and light availability were more critical. This study demonstrates that N enrichment favors the dominance of homeostatic species, while mowing promotes species with plastic nutrient economies. The divergent, species-specific relationships between biogeochemical niche dynamics and biomass highlight the potential value of multi-elemental composition as a tool for understanding plant performance under global changes, and suggest that such trait-based approaches may offer insights into species-specific assembly processes warranting further community-level investigation.

Key words: biogeochemical niche, elemental composition, mowing, niche hypervolume, N enrichment, resource use strategy