Variability in growth-determining hydraulic wood and leaf traits in Melia dubia across a steep water availability gradient in southern India

In India, short-rotation plantations have increasingly been promoted over the last decades in response to altered forest management policy and increased wood demand. Understanding how short-rotation forest species coordinate fast growth with water demand and carbon investment will help improving management decisions. We investigated the intra-specific variability in growth performance, leaf traits, and wood anatomical and derived hydraulic properties in 31 Melia dubia (Meliaceae) plantations along a steep rainfall gradient from 450 to 1,700 mm yr 1, and addressed the role of different irrigation practices and soil nutrient availability. We found water supply and soil nutrient status to have a dominant influence on the aboveground biomass increment (AGBI) of M. dubia. AGBI was higher at irrigated sites with a less negative climatological water balance (i.e. with lower rainfall) and at sites with higher soil phosphorus availability. Stem wood anatomical traits associated with the water transport capacity mirrored the patterns in AGBI. At sites with higher water and soil phosphorus availability, the xylem was composed of larger vessel diameters and lower vessel densities. However, both branch wood anatomical traits and leaf traits including the leaf-to-sapwood area ratio were largely independent of water availability and soil conditions. We conclude that a high stem hydraulic efficiency determined by large xylem vessels is a prerequisite for high aboveground productivity, and that the growth of M. dubia may often be phosphorus-limited. Short-rotation plantations with M. dubia will therefore clearly benefits from continuous irrigation in regions that receive annual precipitations substantially below 1,000 mm yr 1. This highlights the potential to increase yields in this important short-rotation forest species by improving irrigation and fertilization protocols.

Automated summary

Short-rotation plantations of Melia dubia in India are affected by water supply and soil nutrient status, with phosphorus limitation potentially influencing growth. Sites with higher water and phosphorus availability show higher hydraulic efficiency in stem wood anatomical traits. Branch wood anatomical traits and leaf traits, however, seem to be less influenced by water and soil conditions.