Plasticity of Leaf Hydraulic Conductance in Maize in Response to Varying Nitrogen and Water Supplies

The availabilities of nitrogen (N) and water are two important environmental factors affecting crop growth and productivity in the dryland farming, how they affected leaf water transport capabilities, a bottleneck of whole-plant water transport, was seldom studied. So, the effects of different N and water supplies on leaf hydraulic conductance (Kleaf) in maize (Zea mays L.) were studied by a pot experiment, Kleaf, leaf gas exchange, vein traits and other physio-anatomical traits were measured. We found Kleaf was strongly coupled to leaf gas exchange (net photosynthetic rate, Pn, and stomatal conductance, gs) and whole-plant performance under varying N and water supplies. Long-term N supply had a greater impact than irrigation on Kleaf, Pn and gs due to the type and duration of stress, and the N and water treatments did not interact with these physiological parameters. Kleaf was related positively with the xylem conduit diameter of large longitudinal veins, the proportion of minor-vein length and interveinal distance of large and intermediate longitudinal veins, and negatively with the density of the major veins, and the interveinal distance of the transverse veins. The higher Kleaf under ambient N and water supply was also associated with larger leaf area, leaf mass per area and N content per leaf area and with an improved status of leaf water, which partly enhanced the vein traits responsible for the higher Kleaf. These results are helpful to understand leaf hydraulic strategy in adapting to long-term resource deficiency.