Coordinated seasonal changes in leaf dry mass, leaf photosynthetic rate and vessel formation in diffuse-porous Fagus crenata and ring-porous Quercus crispula trees

Abstract

Among broadleaf deciduous trees, diffuse-porous and ring-porous species differ in anatomical vessel distributions, influencing the seasonal timing of vessel formation, leaf growth, and stored carbon use in early spring. This study investigated the seasonal coordination of leaf mass, photosynthesis, starch storage, and xylem formation in shoots and stems of mature trees of coexisting diffuse-porous Fagus crenata Blume and ring-porous Quercus crispula Blume. We also characterized the thermal conditions associated with key phenological events using growing degree days (GDD). Vessel formation in shoots of both species began before bud burst, suggesting reliance on stored carbon. During the leaf developmental period, shoot starch levels declined after bud burst and rose again with increasing photosynthesis, supporting a sink-to-source transition in leaves. In Q. crispula stems, vessel formation progressed concurrently with increases in leaf mass and photosynthesis, demonstrating coordination among these processes. In contrast, vessel formation in F. crenata stems occurred after the leaf developmental period, indicating reliance on current photosynthates. The GDD at which stem vessel formation began was substantially lower in Q. crispula (174–255) than in F. crenata (437–691), whereas GDD values for shoot-level events were similar between species. Importantly, vessel formation appears to be coordinated with leaf development at different organizational levels between species: in shoots of F. crenata and in stems of Q. crispula. Our findings underscore species-specific coordination between anatomical development and physiological processes, reflecting adaptive strategies in water and carbon use during spring growth.