Effects of photochemical oxidants on Japanese forest tree species under elevated CO_2 concentration

在日本群马县前桥县的两个生长季节，对2年生的白桦、3年生的白桦、2年生的赤松和柳杉幼苗进行了臭氧(O_3)和二氧化碳(CO_2)的暴露。用10个开顶式气室对过滤空气(FA)、环境空气(1.0x环境O_3)、高O_3(1.5x环境)、高CO_2(1.5x环境)、高O_3和CO_2 5种气体进行处理。在环境CO_2浓度下，随着O_3浓度或剂量的增加，4种树种的干重增长显著降低。另一方面，与在环境CO_2浓度下生长的苗木相比，在高CO_2浓度下生长的4种树种的干重增长显著增加。O_3和CO_2处理对德国白桦、密花白桦和日本白桦的生长和光合作用参数没有显著的交互作用，但对白桦的生长和光合作用参数有显著影响。CO_2浓度升高对O_3诱导的白桦干重生长和净光合作用下降的影响是相反的，而对其他三种树种则不起作用。研究结果表明，不同树种对O_3和CO_2浓度升高的生长和光合作用响应不同。

Two-year-old Betula platyphylla Sukatchev var.japonica, three-year-old Betula ermanii Cham., two-year-old Pinus densiflora Sieb.et Zucc.and Cryptomeria japonica D.Don seedlings were exposed to ambient or elevated ozone (O_3) and carbon dioxide (CO_2) during two growing seasons in Maebashi, Gunma Prefecture, Japan. Ten open-top chambers were used for five different gas treatments : filtered air (FA), ambient air (1.0x ambient O_3), elevated O_3(1.5x ambient), elevated CO_2 (1.5x ambient), and elevated O_3 and CO_2. At ambient CO_2 concentration, the dry weight growth of the four tree species was significantly reduced with increasing the concentration or dose of O_3. On the other hand, the dry weight growth of the four tree species grown at elevated CO_2 concentration was significantly increased as compared with that of the seedlings grown at ambient CO_2 concentration. Significant interactions between O_3 and CO_2 treatments could not be found on the growth and photosynthetic parameters of B.ermanii, P.densiflora and C.japonica, but on those of B.platyphylla. The effects of elevated CO_2 concentration on the O_3-induced reductions in the dry weight growth and net photosynthesis were counteractive in B.platyphylla, while not in the other three tree species. The results obtained in the present study indicate that the growth and photosynthetic responses to elevated O_3 and CO_2 concentrations are different among the tree species.