THE EFFECT OF SIMULATED ACID-RAIN ON PINE NEEDLE AND BIRCH LEAF LITTER DECOMPOSITION

The effects of simulated acid rain at pH3 and pH4 (each made from H2SO4 and HNO3) on the decomposition of Scots pine needle litter and mountain birch leaf litter were studied in a field experiment in N Finland. The effects of irrigation were tested by having "dry' control plots receiving only ambient rain, and irrigated controls receiving similar amounts of water to the acid treatments. Treatments and the vegetation type in the plots had significant main effects on mass loss of pine needle litter. Differences between dry and irrigated controls, and the lower mass loss in plots with drier vegetation types showed the importance of moisture conditions in regulating pine litter decomposition. The effects of acid rain treatments on pine litter decomposition were more subtle than those of irrigation. In the moistest vegetation type there was no decrease in mass loss due to acid treatments, but mass loss rates in late stages of decomposition were slightly reduced by acid treatments on the drier plots. Birch litter decomposition was significantly retarded in acid treated plots compared to the irrigated ucontrols during the 2nd year of incubation in one experiment. In the other experiment there was a similar trend, although not significant. At the end of the experiments the difference in mass loss between acid treatments and irrigated controls was 2-5% units. -from Authors