Harmful effects of radicals generated in polluted dew on the needles of Japanese Red Pine (Pinus densiflora)

The effects of free radicals, . OH and . NO, generated in polluted dew wate r on needles of Pinus densiflora (Japanese Red pine) were investigated. . OH-generating solutions (HOOH with Fe(III) and oxalate ion; . OH treatmen t) and . OH- and . NO-generating solutions (NO2-; OH/. NO treatment) were r egulated at 25, 50 and 100 mu mol and pH 4.4. HOCH only (HOOH treatment) wa s used as a control solution. Solutions were applied as a mist to the needl e surface of P. densiflora seedlings before dawn twice a week for 3 months. Within a month, net photosynthesis at near saturating irradiance (Pn) and s tomatal conductance (gl) of . OH-treated needles decreased with increasing solution concentration. The HOCH treatment had no effects on any of the mea sured parameters. Therefore, . OH in the artificial dews caused the decreas es in Pn and gl. In . OH/. NO-treated needles, gl increased during the expe riment, but Pn was unchanged. In all experiments, the characteristics of PS II were not significantly altered. Free radicals in polluted dew water have harmful effects on the photosynthe sis of P. densiflora and compound effects of . OH and . NO are different.