Seasonal Changes in Interclone Variation Following Ozone Exposure on Three Major Gene Pools: An Analysis of Cryptomeria Japonica Clones

Abstract

Recently, there has been a continuous increase in the concentration of tropospheric ozone in urban forests in Japan. Since monoterpenes are precursors to ozone, we need to evaluate the effects of ozone exposure on all tree species that are considered to be sources of monoterpenes. Cryptomeria japonica, which is the most widely planted afforestation tree, is classified into three different gene pools. However, the interclone variation for seasonal changes in the ozone exposure effect has not been evaluated. Thus, free-air ozone enhancement experiments were conducted using three representative clones of C. japonica in the summer and winter. After exposure to twice the ozone concentration in the ambient atmosphere, the effect on the monoterpene emission rate was found to be considerably different among the clones and for the different seasons. The monoterpene emission rate after ozone exposure increased in winter and summer in the native clones (Donden and Yakushima) in the snow area and heavy rain area, respectively. Since monoterpenes are antibacterial substances, each clone adapted sensitivity to stress during each season upon considerable damage. These results suggest that not only differences between tree species but also differences between clones are important for evaluating seasonal variation characteristics after ozone exposure.