Negative effects of hydroxyl radical‐generating mists (simulated dew water) on the photosynthesis and growth of Japanese apricot seedlings ( Prunus mume )

The hydroxyl (OH) radical, which is generated in polluted dew water on leaf surfaces of the Japanese apricot ( Prunus mume ), is known to be a potent oxidant. In order to investigate the effects of the OH radical formed in polluted dew water on the photosynthesis and growth of 3‐year‐old seedlings of P. mume , OH radical‐generating solutions simulating polluted dew water were sprayed in the early morning as a mist throughout a growing season onto the leaf surfaces of seedlings growing in experimental greenhouses. Four OH radical‐generating solutions (0, 6, 18 and 54 μM H 2 O 2 with Fe(III) and an oxalate ion) were used in the mist treatment. Five months after the beginning of treatment, the leaves exposed to the mist containing 54 μM H 2 O 2 showed a significantly smaller maximum CO 2 assimilation rate ( A max ) and stomatal conductance ( g s ) as compared to the leaves exposed to the mist containing 0 μM H 2 O 2 . Exposure of P. mume seedlings to the OH radical‐generating mist had caused a reduction in the dry weight and relative growth rate (RGR) of the above‐ground parts (stem + branch) at the end of the growing season. A significant positive correlation was shown between RGR and A max . Thus, the effects of oxidants generated in polluted dew water on leaf surfaces can be considered to be a cause of the decrease in leaf photosynthesis and growth of P. mume .