Contrasting responses of hydraulic traits between leaf and branch to 16-year nitrogen addition in a larch plantation

Abstract Nitrogen (N) deposition can influence tree hydraulic architecture and water relations that interactively affect tree growth and forest productivity, but responses of tree hydraulic traits to long-term N addition are poorly understood. Here, we examined the effects of 16-year N addition on the hydraulic traits of both leaves and branches of Larix gmelinii in northeastern China. We found that N addition decreased the hydraulic conductivity and vulnerability to cavitation of branches, which were associated with a positive response of the wood density. Conversely, N addition significantly increased the hydraulic conductance and vulnerability to cavitation of leaves. A trade-off between hydraulic efficiency and safety was observed in both leaves and branches. N addition induced a stronger vulnerability segmentation compared to the control trees, implying that the larch trees may acclimate to long-term N addition with a safer hydraulic strategy. Overall, our findings of the contrasting responses of the hydraulic traits between the leaves and branches and the increased vulnerability segmentation to the long-term N addition may be beneficial for the larch trees to adapt to the escalating global N deposition and climate change.