Clonal and site variation of vessels in 7-year-old Eucalyptus globulus

Abstract

Pith to bark variation of vessel anatomy was studied in 17 clones of 7-year-old Eucalyptus globulus trees grown on two sites in Portugal. Vessels were measured by image analysis on transverse microsections cut from radial strips sampled at 25% tree height. The mean vessel area increased gradually from pith to bark, whereas the vessel frequency (number of vessels per unit area) decreased outwards from the innermost ring on and levelled off towards the bark. The proportion of vessels relative to other tissues remained constant across the radius. The vessel variables showed cyclic variations defined by minima (vessel area and proportion) or maxima (number of vessels). The effect of site and clone on vessel variability was significant. Clonal variation accounted for 30% and site explained 67% of the total variance of vessel proportion. At the least water stressed site, vessels appeared to be generally larger and occupied a greater proportion of total cross-sectional area.