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

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.