Effects of SO2 exposure with nitrogen and sulphur fertilization on the growth of Agropyron smithii.
A native Montana grassland was exposed to 3-monthly median SO2 concentrations (52, 131 and 228 mu g/m3) and to N, S and N + S fertilization. Leaf area of live and dead material and litter production were measured throughout the growing season. SO2 exposures significantly increased leaf area only in the 52 mu g/m3 SO2 treatment. Av. number of leaves/plant paralleled live leaf area responses to SO2, emphasizing the balance between fertilization and toxicity rather than SO2-enhanced cell division. With N fertilization, growth increased as the level of SO2 increased, indicating that N fertilization can ameliorate the effects of SO2 pollution. Rate of senescence was more rapid and time of senescence was earlier for N-fertilized plants exposed to 228 mu g/m3 SO2 compared with those exposed to 73 or 134 mu g/m3 SO2, but only rate of senescence increased compared with the control. The rate of senescence was more rapid with N fertilization without SO2 compared with the control. No interaction between soil sulphate and SO2 conc. was observed, even though SO4-fertilizer application rates were high.