Summary We

investigated seasonal patterns of water rela-tions in current-year leaves of three evergreen broad-leaved trees (Ilex pedunculosa Miq., Ligustrum japonicum Thunb. and Eurya japonica Thunb.) with delayed greening in a warm-temperate forest in Japan. We used the pressure-volume meth-od to: (1) assess the extent to which seasonal variation in leaf water relations is attributable to leaf development processes in delayed greening leaves versus seasonal variation in environ-mental variables; and (2) investigate variation in leaf water re-lations during the transition from the sapling to the adult tree stage. Leaf mass per unit leaf area was generally lowest just after completion of leaf expansion in May (late spring), and increased gradually throughout the year. Osmotic potential at full turgor (Ψoft) and leaf water potential at the turgor loss point (Ψwtlp) were highest in May, and lowest in midwinter in all species. In response to decreasing air temperature, Ψo ft dropped at the rate of 0.037 MPa °C–1. Dry-mass-based water content of leaves and the symplastic water fraction of total leaf water con-tent gradually decreased throughout the year in all species. These results indicate that reductions in the symplastic water fraction during leaf development contributed to the passive concentration of solutes in cells and the resulting drop in winter Ψo ft. The ratio of solutes to water volume increased in winter in current-year leaves of L. japonicum and E. japonica, indicating that osmotic adjustment (active accumulation of solutes) also contributed to the drop in winter in Ψo ft. Bulk modulus of elas-ticity in cell walls fluctuated seasonally, but no general trend was found across species. Over the growing season, Ψo ft and Ψw tlp were lower in adult trees than in saplings especially in the case of I. pedunculosa, suggesting that adult-tree leaves are more drought and cold tolerant than sapling leaves. The ontogenetic increase in the stress resistance of I. pedunculosa may be related to its characteristic life form because I. pedunculosa grows taller than the other species studied