Physiological effects of hydroxyl radical (·OH) generating solution as simulated dew on the needle surfaces of Japanese red pine (Pinus densiflora Sieb. et Zucc.)

To investigate the effects of aqueous phase oxidants on the needle gas exchange of pine seedlings, simulated dew waters generating hydroxyl radicals (·OH) were sprayed onto the needle surfaces of pine seedlings. The nutrient contents and amounts of epicuticular wax of pine needles were also determined as a parameter with the effects of ·OH-generating solutions on gas exchange of pine needles. Two different sources and two different photoformation rates of ·OH-generating solutions, photo-Fenton reagents (100 and 200 μM HOOH- 1 μM Fe(III)- 5 μM oxalate) and 100 and 200 μM N(III), were sprayed three times a week in the early mornings for 3.5 months. The results showed that maximum CO₂ assimilation rates (A _max) of pine needles treated with the two photo-Fenton reagents and 100 μM N (III) were smaller than those treated with a control solution after treatment; this did not occur with 200 μM N (III). Mg and Ca contents in the needles had positive correlations with A_max among treatments. Amounts of epicuticular wax differed little among treatments. These results implied that needle nutrient status is one of the factors in reductions in A _max of pine needles treated with ·OH-generating solutions.