Artificial defoliation soon after full leaf expansion leads to reduced shoot hydraulic conductance but constant leaf-specific conductivity in Fagus crenata Blume

Key message

Hydraulic architecture and conductivity of current-year shoots of Japanese beech trees are closely related to the leaf area soon after full leaf expansion.

Abstract

To assess the impact of artificially reducing leaf area at two time points after full leaf expansion on the stem xylem hydraulic architecture and conductivity of current-year shoots in Fagus crenata, we manipulated leaf area by partially cutting the leaves in various proportions of potted beech trees at different times. The reduction in leaf area soon after full leaf expansion resulted in a decrease in the mean vessel diameter, number of vessels, and sapwood area of current-year shoots. Simultaneously, it increased vessel density, leading to a proportional decrease in hydraulic conductivity (K_h) and xylem-specific hydraulic conductivity (K_S). However, the leaf-specific hydraulic conductivity (K_L) of current-year shoots remained unchanged, irrespective of the reduction in leaf area. In contrast, the artificial reduction of leaf area one month after full leaf expansion increased K_L but did not significantly affect the mean vessel diameter, number of vessels, vessel density, sapwood area, K_h, and K_S. These results suggest that the stem xylem hydraulic architecture and conductivity of current-year shoots in Japanese beech are closely related to leaf area soon after full leaf expansion.