Coordination of plant functional traits under nitrogen deposition with phosphorus addition in a desert steppe...

Understanding how plant functional traits respond to nutrient enrichment becomes more crucial for predicting changes in grassland community composition and functions under global changes. However, it remains unclear how nitrogen (N) and phosphorus (P) additions jointly influence a variety of leaf traits and how they coordinate with contrastingly adaptive mechanisms in arid ecosystems. A two-year field experiment with five N levels and two P treatments was conducted to examine the effects of N and P additions on leaf/community functional traits in a desert steppe. We found N addition significantly affected the other six leaf morphological and nutrient traits except leaf thickness (LT); nitrogen addition remarkably increased leaf nitrogen concentration (N_mass) and decreased C/N with or without P; nitrogen addition profoundly elevated stomatal conductance (g_s) but did not obviously affect photosynthetic rate (A_area) except Tribulus terrestris. Compared to grasses, the annual forb T. terrestris exhibited stronger competitiveness (N_mass, A_area) with increased N application. Nitrogen addition obviously increased community-weighted means (CWMs) of N_mass, specific leaf area (SLA), plant height, g_s and A_area, improving aboveground biomass (AGB), whereas P addition significantly enhanced CWM of SLA but reduced CWMs of transpiration rate and LT. With increasing N addition rates, dominant S-strategy species (higher LT and C/N) in low-nutrient environments were gradually substituted by R-strategy species (higher N_mass and A_area) in high-nutrient environments. Our results highlight differential responses of plant functional traits to nutrient enrichment and divergent adaptive strategies among species should be considered when assessing the impacts of global environmental changes on community assembly and functioning.