SALT 



Seedlings were placed in a separate watering tray and watered 

 every 2 to 3 days for 7 weeks with a 1.2 percent (12,000 ppm) 

 solution of NaCl according to Spotts and others (1972). Salt-free 

 water then was applied for the duration of the experiment. 



DROUGHT 



Water was withheld from the seedlings for 22 days, at which 

 time needles showed obvious visible symptoms of moisture 

 stress. Normal watering then was resumed. 



SIMULATED WINTER DRYING 



A sheet of 1/2-inch (1.26-cm) thick plywood was fitted to the 

 top of a chest-type freezer. Holes were cut large enough in the 

 wood to allow insertion of the lower portion of the pots; the pot 

 lip prevented the container from falling through the hole. The 

 freezer lid was left open, the board was placed over the opening, 

 and the pots with seedlings were inserted (fig. 1 ). Freezer temper- 

 ature was maintained at 0° F (-18° C), effectively freezing the 

 soil and seedling roots while the tops remained at greenhouse 

 temperature. Soil and freezer temperatures were monitored 

 daily. After 3 days of freezing, a small oscillating fan was placed 

 about 8.2 ft (2.5 m) from the freezer; the fan cast a light breeze 

 over the seedlings. Except for the relatively high greenhouse 

 temperatures, this treatment simulated winter drought condi- 

 tions. Foliar chlorosis appeared 2 days later and the treatment 

 was discontinued. The pots then were placed in the normal 

 greenhouse environment. 



Figure 1 .—Apparatus used to induce winter dry- 

 ing. The pot bases were subjected to freezing 

 temperatures, freezing the soil and root sys- 

 tems, while the stems and needles were main- 

 tained at greenhouse temperature. A light 

 breeze generated by a small fan directed over 

 the seedlings completed the winter drying 

 simulation. 



SULFUR DIOXIDE 



Seedlings were placed in the chamber described for the control 

 treatment. Sulfur dioxide was obtained from Matheson Gas Co. 

 in a pressurized tank at 1 percent S0 2 in air. Tank S0 2 was 

 diluted with charcoal-filtered air through a mass flowmeter to 



achieve 5 ppm V/v in the airstream to the chamber. Air was sup- 

 plied through a Worthington air compressor; flow was measured 

 with a Matheson #605 Flowmeter. Chamber concentrations were 

 not directly measured for sulfur dioxide nor for any of the other 

 gas treatments. Corrections for barometric pressure and air tern - 

 peratures were made as needed. Flow rate was maintained at 

 1 .77 ft •Vmin (50 1/min) until symptoms appeared on the needles, 

 about 6 hours later. Seedlings were then removed to the normal 

 green house environment. 



HYDROGEN SULFIDE 



Hydrogen sulfide was obtained from Matheson in a pressur- 

 ized tank at 1 .20 percent in helium. The gas was delivered to the 

 seedlings at 50 ppm for 8 hours as described for S0 2 . 



ETHYL MERCAPTAN 



Ethyl mercaptan was obtained from Matheson at 1.28 percent 

 in pure nitrogen and administered to the plants for 10 hours at 50 

 ppm as described for S0 2 . 



HYDROGEN FLUORIDE 



Hydrogen fluoride at 1 13 ppm in air was obtained from 

 Matheson and delivered to the plants at 5 ppb as described for 

 S0 2 . Injury appeared within 3 hours and the seedlings were 

 removed from the chamber to the normal greenhouse 

 environment. 



Symptomatic current-year needles from each of the treatments 

 were collected within 2 weeks of injury. Specimens were killed 

 and fixed in formalin-acetic-alcohol (FAA), dehydrated through 

 tertiary butyl alcohol, and embedded in paraffin (Johansen 

 1940). Serial longitudinal and transverse sections of the entire 

 transition zone were cut to 4.72 x 10^ 4 inch (12 microns) 

 thickness on a rotary microtome, stained with a Feulgen's and 

 fast-green schedule, and observed and photographed through a 

 phase-contrast microscope. The transition zone is the more or 

 less gradual boundary between and including green and necrotic 

 needle tissue. Thus, the serial sections included necrotic, chlo- 

 rotic, and green tissue. This is the region in which one would ex- 

 pect to observe developmental symptoms of internal injury to 

 needle tissues and to have the greatest probability of noting dif- 

 ferences between injuries caused by different agents. 



Field Study 



To determine whether conifer foliage in field situations 

 developed symptoms similar to those observed in the laboratory 

 study, representative necrotic needles of various ages were col- 

 lected from trees near seven industries known to emit phytotoxic 

 gases and from trees in two areas damaged by winter drying. 

 Sampling locations, major abiotic agents, sample size, and 

 species are shown in table 1 . 



Necrotic needles in fluoride-polluted ecosystems were col- 

 lected near an aluminum plant at Columbia Falls, Mont.; near 

 two aluminum plants in the Rhone Valley of Switzerland; and 

 near a phosphorus plant at Ramsay, Mont. Conifer needle 

 samples within sulfur dioxide-polluted areas were collected 

 near a lead smelter at Helena, Mont., and a copper smelter at 

 Anaconda, Mont. Needles presumably injured by hydrogen 

 sulfide were collected near a geothermal complex in California. 

 Conifer foliage injured by a complex of sulfur dioxide, hydrogen 



2 



