Photosynthetic response of early and late leaves of white birch (Betula platyphylla var. japonica) grown under free-air ozone exposure.
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.
Silviculture and Forest Ecological Studies, Hokkaido University, Sapporo 060-8689, Japan. Electronic address: ahoshika@for.agr.hokudai.ac.jp.
Yasutomo
Y
Hoshika
Makoto
M
Watanabe
Naoki
N
Inada
Qiaozhi
Q
Mao
Takayoshi
T
Koike
D000393:Air Pollutants / Q000633:toxicity*; D029662:Betula / Q000187:drug effects* / Q000502:physiology; D007564:Japan; D010126:Ozone / Q000633:toxicity*; D010788:Photosynthesis / Q000187:drug effects* / Q000502:physiology; D018515:Plant Leaves / Q000187:drug effects* / Q000502:physiology; D012621:Seasons
D000393:Air Pollutants; D010126:Ozone
Heterophyll; Photosynthesis; Tropospheric ozone; White birch (Betula platyphylla var. japonica)