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

2年生白桦、3年生岳桦、Sieb.et日本群马县前桥市，将2年生赤松（Pinus densiflora）和柳杉（Cryptomeria japonica D.Don）幼苗在两个生长季节暴露于环境或高浓度的臭氧（O_3）和二氧化碳（CO_2）中。10个开顶室用于五种不同的气体处理：过滤空气（FA）、环境空气（1.0 ×环境O_3）、升高的O_3（1.5 ×环境）、升高的CO_2（1.5 ×环境）以及升高的O_3和CO_2。在大气CO_2浓度下，随着O_3浓度或剂量的增加，4种树种的干重生长量均显著降低。另外，在高CO_2浓度下生长的4个树种幼苗的干重生长量均显著高于在正常CO_2浓度下生长的幼苗。O_3和CO_2处理对艾氏B.ermanii、密花杨和龟背竹的生长和光合参数没有显著的交互作用，但对白桦的生长和光合参数有显著的交互作用。CO_2浓度升高对O_3引起的白桦干重生长和净光合速率的降低有抵消作用，而对其它3种树种则无影响。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反应不同。

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.