Impacts of Ambient Ozone and/or Acid Mist on the Growth of 14 Tree Species: An Open-Top Chamber Study Conducted in Japan

Young trees of 14 species were exposed to ambient ozone (O₃), (charcoal-filtered air [CF] or non-filtered air [NF]) and/or acid mist (pH 5 or 3 : SO₄2, NO₃, Cl- at equivalent 1:2:1 ratio) over three seasons (from June 1993 to November 1995) using tunnel-type open-top chambers at two sites (Abiko: 25 ma.s.l. and Akagi: 540 m a.s.l.)in Japan. Ambient, 12-hr (0600-1800) mean O₃ concentration for April-September during the period of experiment at Akagi (41 ppb) was 40% higher than that at Abiko (30 ppb). The NF- and CF-chambers had 90% and 30% of ambient O₃, respectively. Significant decreases in biomass in the NF treatments were observed in Pinus densiflora, Larix kaempferi, Picea abies, Abies firma, Abies homolepis, Abies veitchii, Cryptomeriajaponica, Populus maximowiczii, Betula platyphylla, Fagus crenata and Zelkova serrata as compared with the CF treatment. These results indicate that the current ambient level of O₃ in Japan is high enough to have adverse effects on the growth of all tree species examined, except Pinus thunbergii, Chamaecyparis obtusa and Quercus mongolica. Increasing acidity of mist caused no growth decreases in all tree species examined However, the growth decreases by O₃ were greater at pH3 mist treatment than at pH 5 mist treatment on Abies veitchii and Fagus. this suggested that the O₃ effect on tree growth can be exacerbated by the deposition of acid mist, possibly associated with nitrate.