Nitrogen addition alters leaf and root functional traits and their coordination of Populus ussuriensis with different ploidy

Leaves and roots are important resource acquisition organs for plants, and their traits reflect the ecological strategies that enable plants to adapt to environmental changes. Polyploid plants exhibit enhanced adaptability to variations in nitrogen (N). However, studies investigating the effects of N addition on plants often overlook the coordination of leaf and root traits, particularly across different ploidy levels. This study focused on one-year-old homodiploid, triploid, and tetraploid cutting seedlings of Populus ussuriensis to examine the effects of N addition on 18 functional traits of leaves and roots. Our aim was to explore the adaptive strategies of poplar at different ploidy levels in response to N addition, with a particular focus on the trade-offs between leaves and roots. We found that high-ploidy individuals exhibited more acquisition traits compared to diploids following N addition. Specifically, following N addition, low-ploidy P. ussuriensis showed increased leaf photosynthetic productivity, while root functional traits became more conservative. In contrast, high-ploidy individuals adopted a synergistic strategy, simultaneously acquiring resources from both leaves and roots, characterized by increased net photosynthetic rate, leaf area, enhanced absorptive root length, and N uptake rate. Furthermore, N addition shifted the centrality of the trait network from root functional traits to leaf functional traits, thereby ensuring a sustained supply of carbon necessary for plant growth. These findings indicate that polyploids exhibit significant growth advantages in N-enriched environments, which can be attributed to the synergistic enhancement of both root and leaf traits. A conceptual model showing the responses of leaf and root functional traits and their coordination in relation to nitrogen addition. Nitrogen addition prompted a shift in the traits of high-ploidy leaves and roots towards more acquisitive values. Conversely, the traits of low-ploidy leaves and roots exhibited a trade-off following nitrogen addition. In terms of the trait network, nitrogen addition altered the network's centrality from root nitrogen concentration to specific leaf area, while also decreasing the overall connectedness of the trait network. These changes in plant trait characteristics may confer an adaptive advantage to polyploid plants in response to atmospheric nitrogen deposition. The trait abbreviations are: SLA: Specific leaf area, LMA: Leaf mass per area, LN: Leaf nitrogen concentration, aR: absorptive root. • Integrated the nitrogen uptake rate into the root economic space. • Nitrogen addition prompted more acquisitive traits in high-ploidy leaves and roots. • low-ploidy leaf and root traits exhibited a trade-off in response to nitrogen addition. • Nitrogen addition altered the centrality of the network from root traits to leaf traits.