Abstract: Aims The objective of this study was to determine whether leaf stoichiometry is predominantly shaped by habitat filtering or phylogenetic conservatism in the extreme dry-hot valley of the Jinsha River. We further evaluated the applicability of the biogeochemical niche and stoichiometric plasticity hypotheses at a regional scale. Methods We collected 240 leaf samples from 13 shrub and herbaceous species at 5 sampling sites along the Jinsha River. Leaf carbon (C), nitrogen (N), and phosphorus (P) stoichiometric traits were measured. Corresponding soil physicochemical properties were also analyzed.Bayesian phylogenetic linear mixed models were used to quantify the relative contributions of habitat factors and phylogeny to variation in leaf stoichiometry, and to explore how major habitat gradients regulate plant nutrient use strategies. Important findings Habitat factors collectively explained 1.9 to 13.7% of the variability in leaf elements and their stoichiometric ratios. Elevation was the primary driver of leaf C, P, C:P, and N:P ratios, whereas soil pH was the main regulator of leaf N and the C:N ratio. Importantly, significant phylogenetic signals were observed in leaf N, P, C:N, and C:P ratios, indicating the conservatism of these traits. In addition to phylogenetic constraints, we found that leaf C concentration was primarily associated with plant life form and the N:P ratio showed greater intraspecific plasticity. In conclusion, regional leaf stoichiometric patterns were governed mainly by phylogenetic conservatism and refined by phenotypic plasticity. These findings enhance our understanding of how plant diversity is maintained under habitat stress and broaden knowledge of plant nutrient-use strategies at regional scales.

Key words: Leaf stoichiometry, Phylogeny, Phenotypic plasticity, Habitat filtering, Dry-hot river valley