Growth, photosynthesis, and chlorophyll concentrations of red spruce seedlings treated with mist containing hydrogen peroxide

The effects of controlled exposures of mist (50-90 μm drop size) containing hydrogen peroxide (H₂O₂) on greenhouse-grown red spruce (Picea rubens Sarg.) were studied for 16 wk coincident with the 1987 growing season. One-year-old seedlings were treated with simulated mist containing 0, 15, 59, or 235 μM H₂O₂ three times each week from 2400 to 0930 h. Height, diameters, net photosynthesis, respiration, chlorophyll, and dry weight measurements were made. After 16 wk of H₂O₂ exposures, no visible symptoms of foliar injury were evident. Similarly, no differences in net photosynthesis, respiration, or needle pigment concentrations were observed. Analysis of covariance of the dry weight data showed significantly greater dry matter in seedlings exposed to 235 μM H₂O₂ treatment vs. those treatments representing a range of ambient conditions (0, 15, and 59 μM). Mean relative growth rates were also the greatest for seedlings of the 235 μM treatment. Given these controlled exposure studies, it is hypothesized that concentrations of wet-deposited H₂O₂ of up to twice current ambient maximums are unlikely to reduce red spruce seedling growth through direct impairment of leaf function.