Harayama Hisanori, Ikeda Takefumi, Ishida Atsushi, Yamamoto Shin-Ichi
Laboratory of Forest Ecology and Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya 464-8601, Japan.
Tree Physiol. 2006 Aug;26(8):1025-33. doi: 10.1093/treephys/26.8.1025.
We investigated seasonal patterns of water relations 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 method 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 environmental variables; and (2) investigate variation in leaf water relations 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 (Psi(o) (ft)) and leaf water potential at the turgor loss point (Psi(w) (tlp)) were highest in May, and lowest in midwinter in all species. In response to decreasing air temperature, Psi(o) (ft) dropped at the rate of 0.037 MPa degrees C(-1). Dry-mass-based water content of leaves and the symplastic water fraction of total leaf water content 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 Psi(o) (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 Psi(o) (ft). Bulk modulus of elasticity in cell walls fluctuated seasonally, but no general trend was found across species. Over the growing season, Psi(o) (ft) and Psi(w) (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.
我们调查了日本暖温带森林中三种延迟返青的常绿阔叶树（柄果冬青、日本女贞和杨桐）当年生叶片水分关系的季节模式。我们采用压力-容积法来：（1）评估叶片水分关系的季节变化在多大程度上归因于延迟返青叶片的叶片发育过程，而非环境变量的季节变化；（2）研究从幼树阶段到成年树阶段过渡期间叶片水分关系的变化。单位叶面积叶质量通常在5月（晚春）叶片扩展完成后刚达到最低，并在全年逐渐增加。所有物种的充分膨压下的渗透势（Ψo(ft)）和膨压丧失点的叶水势（Ψw(tlp)）在5月最高，在冬季中期最低。随着气温下降，Ψo(ft)以0.037 MPa·℃-1的速率下降。所有物种叶片基于干质量的含水量和总叶含水量的共质体水分分数在全年逐渐降低。这些结果表明，叶片发育过程中共质体水分分数的降低导致细胞中溶质的被动浓缩以及冬季Ψo(ft)的下降。日本女贞和杨桐当年生叶片中溶质与水体积的比率在冬季增加，表明渗透调节（溶质的主动积累）也导致了冬季Ψo(ft)的下降。细胞壁的弹性模量有季节性波动，但未发现跨物种的一般趋势。在生长季节，成年树的Ψo(ft)和Ψw(tlp)低于幼树，特别是柄果冬青的情况，这表明成年树叶片比幼树叶片更耐旱和耐寒。柄果冬青抗逆性的个体发育增加可能与其独特的生活型有关，因为柄果冬青比其他研究物种长得更高。
