Relationship between vessel porosity and leaf emergence pattern in ring- and diffuse-porous deciduous trees in a temperate hardwood forest

Abstract

To elucidate the functional relationship between intra-annual variations in vessel diameter and leaf emergence pattern of ring-porous and diffuse-porous deciduous trees in temperate forests, we determined the temporal relationships between leaf phenology and vessel formation. Cylindrical stem cores were periodically collected from each of five ring- and diffuse-porous species, and the leaf and vessel formation were observed simultaneously. In the ring-porous species, vessel formation began within 2 weeks of leaf appearance, and most wide vessels were formed within 2 weeks of full leaf expansion. More of the trees with intermediate-type formed medium-sized vessels or sparse wide vessels than trees with the flush-type leaf emergence, especially between full leaf expansion and the end of shoot elongation. Narrow vessel formation began 2–8 weeks after full leaf expansion in all specimens. The transition between the pore- and non-pore zones was abrupt in the flush-type species, and gradual in the intermediate-type species. In contrast, diffuse-porous species formed vessels 0–8 weeks after full leaf expansion. Our findings suggest that ring-porous species form leaves and vessels synchronously to accommodate water-transport requirements, whereas diffuse-porous species form these tissues asynchronously; thus, unlike the latter type, the former species change vessel diameters according to leaf formation.