Water relations and leaf area dynamics in a short-rotation coppice willow plantation during the growing season

In short-rotation coppice (SRC) willow (Salix spp.) bioenergy plantations, productivity is mainly determined by water availability and light interception. Thus, the aims of this work were: to analyse the effects of water availability (irrigated and rainfed), planting density (13,333 and 20,000 plants ha-1) and genotype (two clones with different sensitivity to water availability) on water transport and leaf area development along the season in a SRC willow plantation; and to explore possible physiological mechanisms explaining the difference in water stress susceptibility between the two willow genotypes analysed. Our hypothesis was that the clone with lower sensitivity to drought has a more efficient xylem water transport, is able to perform osmotic adjustment, and is less susceptible to xylem embolism. The clones analysed showed no differences in osmotic adjustment or susceptibility to xylem embolism. Both adjusted their leaf area to the stem water transport capacity, a fact related to stem diameter and affected by the soil water availability. The early leaf development and the higher persistence of leaf area in the late growing season can explain the higher stem diameter and water conductivity in the most drought tolerant genotype.