Effects of simulated acid rain on forest floor microbiological processes were investigated in an old-growth sugar maple (Acersaccharum Marsh.) woods at Turkey Lakes Watershed, northern Ontario, Canada. Sulphate and NO3− in ambient precipitation received on four replicate plots were augmented with additions of dilute (0.02 N) H2SO4 and HNO3, applied alone and in combination periodically during the growing seasons of 1993 and 1994. The equivalent load of SO42− applied in the present experiment was ca. 6 times that in ambient precipitation in the H2SO4-only treatment and half that in the combined treatment over the study period. In situ soil respiration measured during the summer and fall of 1994 showed no adverse effects of acid treatment. In the laboratory, soil microbial respiration, biomass (as determined by substrate-induced respiration), and microbial biomass carbon: organic carbon (Cmic/Corg ratios were significantly depressed in the L or FH layers of the forest floor when H2SO4 was applied alone or in combination with HNO3. No effects of HNO3 were detected when applied alone. Microbial respiration, substrate-induced respiration, and Cmic/Corg ratios were significantly correlated with forest floor pH. Microbial metabolic quotients (respiration:biomass ratios) were not adversely affected by any of the treatments. The observed deleterious effects of H2SO4 application under experimental conditions suggest the possibility of adverse effects in the field over the long-term.
Simulated Acid Rain-induced Alterations in Flowering, Leaf Abscission and Pollen Germination in Sunflower (Helianthus annuus L.)