Silviculture and Forest Ecological Studies, Hokkaido University, Sapporo 060-8689, Japan.
Environ Pollut. 2013 Nov;182:242-7. doi: 10.1016/j.envpol.2013.07.033. Epub 2013 Aug 9.
Betula platyphylla var. japonica (white birch) has heterophyllous leaves (i.e., early and late leaves) and is a typical pioneer tree species in northern Japan. Seedlings of white birch were exposed to ozone during two growing seasons, and measurements were carried out in the second year. Early leaves did not show an ozone-induced reduction in photosynthesis because of lower stomatal conductance resulting in higher avoidance capacity for ozone-induced stress. Also, an ozone-related increase in leaf nitrogen content may partly contribute to maintain the photosynthetic capacity in early leaves under elevated ozone in autumn. On the other hand, late leaves showed an ozone-induced decline of photosynthesis and early defoliation of leaves occurred. Also, smaller leaf size and higher stomatal density in late leaves were observed under elevated ozone. Differences in stress resistance to ozone may be related to differing functional roles of early and late leaves for birch species.
日本桤木（银桦）具有异形叶（即早生叶和晚生叶），是日本北部的典型先锋树种。在两个生长季节中，将臭氧暴露于银桦幼苗上，并在第二年进行测量。由于较低的气孔导度导致早生叶对臭氧胁迫的回避能力更高，因此早生叶没有表现出臭氧诱导的光合作用降低。此外，叶片氮含量的臭氧相关增加可能部分有助于维持秋季高臭氧下早生叶的光合作用能力。另一方面，晚生叶表现出臭氧诱导的光合作用下降和早生叶的早期脱落。此外，在高臭氧下，晚生叶的叶片尺寸较小，气孔密度较高。对臭氧的抗逆性差异可能与银桦属植物早生叶和晚生叶的不同功能角色有关。
