Variation and Trade-Offs in Leaf and Root Traits of Perennial Grasses Under Nitrogen Deposition

Atmospheric nitrogen deposition is increasing globally, making it essential to understand how leaf and root traits vary and interact to shape plant ecological strategies under changing environmental conditions. We conducted leaf and root traits of eight perennial grasses (rhizomatous and bunchgrass species) in a field experiment conducted in the Songnen grassland, incorporating control and nitrogen addition treatments (10 g m−2 yr−1). Nitrogen addition significantly altered leaf and root trait expression and promoted biomass accumulation in both life forms. Specifically, nitrogen addition increased assimilation rate (An; 19.4 and 20.7%), leaf nitrogen content (LNC; 51.5 and 57.8%), specific root length (SRL; 30.1 and 41.1%), and root nitrogen content (RNC; 18.6 and 34.4%), while markedly reducing root tissue density (RTD; 40.2 and 46.6%) of perennial rhizome grass and perennial bunchgrasses. Principal component analysis revealed multiple plant resource strategies reflected by multidimensional variation in leaf and root traits. However, no consistent correlations were detected between leaf and root trait dimensions, and regression relationships differed significantly under nitrogen addition. These results indicate a decoupling of above- and belowground resource acquisition strategies at the local scale. Additionally, we underscore the importance of combining above- and belowground traits to improve predictions of plant performance. Our findings advance understanding of leaf–root trait coordination in perennial grasses and provide insights into plant adaptive strategies in arid and semi-arid regions’ grassland ecosystems experiencing increasing nitrogen deposition.