The adaptive responses of leaf and root traits and metabolites to nitrogen addition promote Dalbergia odorifera growth

Dalbergia odorifera is a key industrial leguminous tree species that provides high-quality timber. Increasing nitrogen (N) deposition and fertiliser application have greatly increased the availability of N to vegetation. Leguminous tree species possess characteristics such as symbiotic nitrogen fixation and higher nitrogen concentrations than other tree species. Therefore, Dalbergia odorifera may exhibit a series of trade-off responses to increased nitrogen. However, the regulatory mechanisms governing its response remain underexplored. We investigated how the growth and leaf and root traits of Dalbergia odorifera responded to nitrogen addition through pot experiments and used meta-analysis to examine the universality of these changes in leguminous trees. In addition, we performed metabolomics and transcriptomics analyses of Dalbergia odorifera leaves and roots to explore the molecular mechanisms underlying these trait changes. The results showed that N application enhanced the leaf N concentration, physiological traits associated with photosynthesis, root biomass, and N concentration, suppressed nodulation, and altered the morphological traits. These traits varied mainly along the first (71.55%) and second components (20.09%), with the first axis strongly linked to increased tree growth. This pattern was further supported by the meta-analysis. Additionally, N addition promoted root growth and N translocation, and suppressed nodulation via N and flavonoid metabolism. The synthesis and metabolism of stored carbohydrates were inhibited to maintain the metabolic balance of C and N. Overall, we highlight the significant contributions of functional traits and metabolic regulation to the N response in Dalbergia odorifera , which may determine leguminous trees survival and growth strategies in N-rich ecosystems.

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