Edge Effects on Carbon, Nitrogen, Phosphorus, and Non-Structural Carbohydrates in Organs of Salsola collina

Plant patches are a common feature of dryland ecosystems, but how within-patch spatial position is associated with plant functional traits-and whether these patterns differ among organs-remains poorly understood. We sampled twigs, leaves, and flowers of the C₄ desert plant Salsola collina from the centers and edges of natural patches in arid Xinjiang, China, using five plots with three patches per plot. For each organ, we measured the concentrations of carbon (C), nitrogen (N), phosphorus (P), sucrose (SUC), fructose (FRU), total soluble sugars (SS), and starch (ST), and calculated non-structural carbohydrate (NSC) concentrations as the sum of SS and ST. Treating the plot as the experimental unit and accounting for paired center-edge observations within plots, we evaluated the effects of patch position, organ type, and their interaction using two-way ANOVA and distance-based multivariate analyses. Organ type accounted for the largest proportion of multivariate trait variation (R² = 0.90), whereas patch position and the Patch × Organ interaction each explained approximately 4% (all p < 0.001). Significant Patch × Organ interactions were detected for 14 of 17 traits, indicating that center-edge differences varied among organs for most traits. N concentrations were higher at patch edges in all three organs, whereas P concentrations were higher in twigs and flowers only; C showed no significant center-edge differences. NSC concentrations were higher at patch edges in all three organs, while SS was higher in edge twigs and leaves and ST was higher in edge flowers. These patterns were accompanied by contrasting organ-specific differences in carbohydrate composition and elemental stoichiometry. Because environmental variables were not measured concurrently, the observed patterns should be interpreted as spatial associations rather than demonstrated environmental mechanisms. These findings indicate that organ identity and within-patch position are jointly associated with variation in the carbon-, nutrient-, and carbohydrate-related traits of S. collina, highlighting the importance of considering organ-specific variation when evaluating fine-scale spatial heterogeneity in dryland plants.