Display omitted •Leaf nutrient fractions indicate the responses of wetland plants to nutrient enrichment.•Responses of leaf N and P allocation patterns to nutrient enrichments were species-specific.•Plasticity in leaf nutrient fractions drives nutrient enrichment-induced shifts in plant biomass.•Leaf nutrient allocation patterns may be a potential indicator of vegetation community composition. Temperate wetlands have been experienced increased nitrogen (N) and phosphorus (P) loadings, but how plant N and P fractions respond to nutrient enrichments and its role in driving vegetation dynamics remain elusive in these ecosystems. Here, we used a 3-year N (6.0 g N m−2 year−1) and P (1.2 g P m−2 year−1) addition experiment to investigate the effects of nutrient enrichment on aboveground plant biomass, leaf N, P, structural N (NS), non-structural N (NNS), inorganic P (PI), and organic P (PO) concentrations of five common species belonging to two growth forms (grass and sedge) in a freshwater marsh, Northeast China. Our results showed that, although leaf N and P concentrations increased with respective nutrient additions, the responses of aboveground plant biomass and leaf nutrient allocation patterns to nutrient enrichments were idiosyncratic. Specifically, N addition simultaneously increased leaf NNS:NN ratio and aboveground biomass of grass species (Deyeuxia angustifolia and Glyceria spiculosa), while P addition increased leaf PI:PO ratio and aboveground biomass of sedge species (Carex meyeriana, C. lasiocarpa, and C. humida). This indicated that the species-specific responses of leaf nutrient fractions to N and P addition may explain the altered vegetation structure in this wetland. Our findings suggest that leaf nutrient fractions are more reliable than total nutrient concentrations to indicate the adaptative strategies of wetland plants to nutrient enrichments, and highlight that the shifts in leaf N and P allocation patterns would be a potential tool to predict the effect of nutrient enrichments on vegetation dynamics in temperate wetlands.