Relative Sensitivity of Pine Species to Ozone

Materials and Methods

Species used were southwestern white pine (Pinus strobiformis), Scotch pine (P. sylvestris), eastern white pine, bristlecone pine (P. aristata), ponderosa pine, Austrian Pine (P. nigra), Japanese black pine (P. thunbergii), jack pine (P. banksiana) and Japanese white pine (F. parviflora). For each species, 28 2-year-old seedlings growing in a peat:perlite:soil mix (2:2:1) in 4.7 I containers were randomly placed (7/chamber/species) in each of 4 cylindrical, open-top field chambers (6), with concentrations of 0, 10, 20, or 30 pphm ozone. Ambient air was filtered through charcoal before entering the chambers. Ozone was generated by passing oxygen through a corona-discharge generator. Ozone concentration was continuously monitored with a Dasibi Model 1 003-AH ozone monitor, and was daily calibrated with a Monitor Labs Model 8500 Permacal Calibrator.¹ Fumigations were carried out 8 hr/day, 5 days/week from early July through September, 1979. Weather conditions were typical for Ohio at that time of year, with moderate extremes of heat and moisture. The percentage of all of the foliage affected by symptoms was recorded weekly or biweekly during the time of fumigation. After treatment, seedlings were transferred to a shade house and mulched for overwintering. Survival of seedlings was recorded in July, 1980.

Results

Analyses of variance of arcsin transformed data indicated significant differences in injury among species and among concentrations within species (Table 1). At the lowest concentration (10 pphm), Scotch pine showed the most injury, with other species showing little or no injury (Fig. 1). Japanese white, Scotch, jack, and ponderosa pines were the species most susceptible to ozone injury at 20 and 30 pphm. Injury to jack pine was low during the first 40 days of fumigation, then increased rapidly until the end of fumigation (Fig. 1). Bristlecone and eastern white pines showed little or no injury at 20 or 30 pphm; and were the most tolerant to ozone. Austrian, southwestern white,and Japanese black pines were also fairly tolerant (Fig. 1).

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Fig. 1.

Foliar symptoms of ozone-treated pine seedlings as excess of control (0 pphm) seedlings at three concentrations. Species used were Pinus sylvestris (sy), P. parviflora (pa), P. banksiana (ba), P. ponderosa (po), P. thunbergii (th), P. nigra (ni), P. strobiformis (ss), P. strobus (st), and P. aristata (ar).

The first symptoms to appear on ozone-fumigated seedlings usually were flecking, mottling, and needle-tip chlorosis. More extensive chlorosis and necrosis later developed on the more sensitive species. Ponderosa, jack, and Scotch pines, for example, showed a diffuse yellowing on the foliage throughout many of the seedlings. By the end of the fumigation period, many of the ozone-treated jack pine needles were completely brown.

Survival of Scotch pine seedlings exposed to 20 and 30 pphm ozone was significantly reduced, as measured by a chi-square test (Table 1). Seedlings exposed to both these concentrations showed only 43 per cent survival (compared to 100% survival of the control seedlings). Survival of the jack pine seedlings was not significantly reduced after fumigation with 20 pphm, but after 30 pphm none of the exposed seedlings had survived by July, 1980. None of the other species or treatments showed a significant decrease in survival, compared to control seedlings.

Discussion

Consistent interspecific differences occurred in the response to ozone of these 9 pine species. Davis and Wood (5) had found 4 of these species to be susceptible to short-term (25 pphm, 8 hr) exposure to ozone, and had ranked them (from most to least susceptible) as: jack, Austrian, Scotch, and eastern white pines. In our study with much longer exposure time, we found Scotch to be much more susceptible than Austrian pine and eastern white to be more tolerant.

Both jack and Scotch pines showed pronounced visible symptoms and also a significant increase in mortality due to ozone. Ponderosa pine showed a consistent increase in injury with length of fumigation time. Phytosynthesis in this species has been reduced 10% by 15 pphm ozone for 30 days (9). The five-needled pine species showed a range from low (bristlecone, eastern white, and southwestern white) to high (Japanese white pine) ozone susceptibility. The 2- and 3-needled species also showed a similar range.

All of these species are planted in or are indigenous to urban and forest areas. More research is needed on within-species variation in response to ozone, as suggested by Davis and Gerhold (4) and as carried out recently on Scotch pine provenances by Weidensaul (10).