Responses of flag-leaf vein traits to nitrogen and water supplies and their correlations with leaf hydraulic-physiological function in wheat

Objectives  Leaf vein traits affect leaf physiological function. We studied the plastic response of the leaf vein traits to different nitrogen and water supplies, and analyzed their correlation with leaf physiological function for demonstrating plant adaptation to different habitats.

Methods  A pot experiment with a three-factor complete random design was conducted. The two wheat cultivars were drought-sensitive Zhengmai 101 and drought-tolerant Changhan 58; the two nitrogen fertilizer levels were 0 and N 0.15 g/kg dry soil before sowing; the three water supplying levels were 70%–75%, 50%–55% and 30%–35% of field capacity at the jointing stage, respectively. After the water treatments were maintained for about 3 weeks, the flag-leaf vein traits major-vein density (VLA_major), minor-vein density (VLA_minor), vein density (VLA) and proportion of minor-vein density (Pro_minor), and the leaf hydraulic-physiological function indices leaf hydraulic conductance (K_leaf), net photosynthetic rate (P_n), stomatal conductance (g_s), transpiration rate (E) and instantaneous water use efficiency (IWUE) were measured.

Results  Drought-tolerant cultivar Changhan 58 had higher VLA_major, VLA_minor, VLA and Pro_minor than drought-sensitive cultivar Zhengmai 101. For Zhengmai 101, VLA_major decreased, VLA_minor and VLA kept unchanged with the increased nitrogen and water supplies, whereas for Changhan 58, VLA_major, VLA_minor and VLA all decreased with the increased nitrogen and water supplies. VLA_minor and VLA of two wheat cultivars showed different responses to N and water supplies. In the twenty correlations between leaf vein traits and leaf hydro-physiological function parameters, five ones of Zhengmai 101 reached significant (P < 0.05) or nearly significant levels (0.05 < P < 0.1), VLA_major was negatively correlated with K_leaf and g_s, and Pro_minor was positively correlated with K_leaf, g_s and E. And for Changhan 58, 14 correlations were significant or nearly significant, VLA_major, VLA_minor and VLA were all negatively correlated with K_leaf, P_n and g_s, VLA_major were negatively correlated with IWUE, VLA_minor and VLA were negatively correlated with E, and Pro_minor was negatively correlated with P_n and E.

Conclusions  Leaf vein traits of drought-tolerant wheat cultivar are sensitive to nitrogen and water supplies, and more closely correlated with leaf hydraulic-physiological functions. Leaf hydraulic-physiological functions will be increased with the higher proportion of minor-vein length in drought-sensitive cultivar, while they will be constrained by vein density and proportion of minor-vein length in drought-tolerant cultivar, suggesting that drought-sensitive cultivar increase its leaf hydraulic-physiological function through optimization of vein length of different types of veins, and the drought-tolerant wheat cultivar through enlarged conduit diameter and extra-xylary hydraulic conductance.