Silviculture and Forest Ecological Studies, Hokkaido University, Sapporo, Hokkaido, 060-8589, Japan.
J Plant Res. 2014 Mar;127(2):339-45. doi: 10.1007/s10265-013-0622-y. Epub 2013 Dec 24.
To study the effects of different periods of ozone (O3) fumigation on photosynthesis in leaves of the Monarch birch (Betula maximowicziana), we undertook free air O3 fumigation to Monarch birch seedlings at a concentration of 60 nmol mol(-1) during daytime. Plants were exposed to O3 at early, late or both periods in the growing season. The light-saturated net photosynthetic rate (A(sat)) in July and August was reduced by O3 exposure through a reduction in the maximum rate of carboxylation (V(c,max)). In early September, on the other hand, despite a reduction in V(c,max), A(sat) was not reduced by O3 due to a counteracting increase in the stomatal conductance. Through the experiment, there was no difference in sensitivity to O3 between maturing and matured leaves. We analyzed the relationship between A(sat), V(c,max) and accumulated stomatal O3 flux (AF(st)). Whereas V(c,max) decreased with increasing AF(st), the correlation between A(sat) and AF(st) was weak because the response of stomatal conductance to O3 was affected by season. We conclude photosynthetic response of Monarch birch to O3 exposure changes with season. This is due to the inconstant stomatal response to O3 but not due to the respose of biochemical assimilation capacity in chloroplasts.
为了研究不同时期臭氧（O3）熏蒸对银桦叶片光合作用的影响，我们采用 60 nmol mol(-1) 的日间浓度对银桦幼苗进行自由空气臭氧熏蒸。植物在生长季节的早期、晚期或两个时期都暴露在臭氧中。7 月和 8 月，臭氧暴露通过降低羧化的最大速率（V(c,max)）降低了光饱和净光合速率（A(sat)）。另一方面，9 月初，尽管 V(c,max) 降低，但由于气孔导度的抵消增加，A(sat) 没有因臭氧而降低。通过实验，成熟和成熟叶片对臭氧的敏感性没有差异。我们分析了 A(sat)、V(c,max) 和积累的气孔臭氧通量（AF(st)）之间的关系。虽然 V(c,max) 随着 AF(st) 的增加而降低，但 A(sat) 和 AF(st) 之间的相关性较弱，因为气孔对臭氧的响应受季节影响。我们得出结论，银桦对臭氧暴露的光合响应随季节而变化。这是由于气孔对臭氧的反应不稳定，但不是由于叶绿体中生化同化能力的反应。
