Effect of SO2 on transpiration, chlorophyll content, growth, and injury in young seedlings of woody angiosperms

Effects of SO2 on transpiration, chlorophyll content, growth, and injury of woody angiosperm seedlings were studied during the first few weeks after germination. Fumigation of silver maple (Acersaccharinum L.) and black locust (Robiniapseudoacacia L.) seedlings with SO2 at 0.75 ppm for 2 to 16 h increased transpirational water loss. As duration of fumigation was increased, the effect of SO2 on increasing transpiration declined. Leaves of silver maple seedlings fumigated with SO2 at 0.75 ppm for 8 to 16 h were injured; those of black locust were not. In another experiment, the adverse effects of SO2 were greater on black locust than on American elm (Ulmusamericana L.) seedlings. Fumigation of young black locust seedlings with SO2 at 2 ppm for 1 or 4 h significantly reduced chlorophyll content, height growth, dry weight increment of roots, and leaf formation. Leaf injury symptoms appeared within 24 h after fumigation with 2 ppm SO2 for 4 h. Fumigation of American elm seedlings with SO2 at 0.5 or 2 ppm for 0.5 to 4 h decreased dry weight increment of roots but did not injure plants or significantly influence chlorophyll content, height growth, or leaf dry weight. Inhibition of dry weight increment of roots was a more sensitive indicator of susceptibility to SO2 than was reduction in dry weight increment of shoots.