The influence of experimental acidification on nutrient release and decomposition rates of needle and root litter in the forest floor

The influence of experimental acidification (diluted H₂SO₄) on mass-loss rates of needle and root litters was investigated in forests of Scots pine, lodgepole pine, Norway spruce and white birch located in a climatic transect through Sweden. Of the two dosages given (32 and 96 kg S ha⁻¹), significant effects on mass-loss rates were observed mainly with the higher dose. When comparing the effect of acid on mass-loss rate of needle litter on all sites together for the whole 3-year period, no effect was seen. By distinguishing the different types of forest and understorey we found a significant general decrease in rate for needle litter of about 8% for the pine forest sites (n = 10). For the spruce sites (n = 8) and the birch sites (n = 2) no significant effects were seen. When considering single sites after 1 year of decomposition, significant effects (rate decrease) were also found for the birch forests. At some spruce sites significant differences in mass-loss rate were seen (both rate increase and rate decrease). When a significant effect was seen its magnitude was found to be dependent on the decomposition rate (soil biological activity) of that site.For root litter the results were less clear. No significance was seen when comparing all sites together or sites of one type of forest. Significant decreases in mass-loss rate after acid treatment were, however, noted for some of the sites after different incubation periods. The patterns of dynamics of the nutrients N, P, S, K and Ca were not affected whereas those of Mg and Mn were and significantly higher release rates were found for these nutrients after acid treatment. The release rates of the nutrients N, P, S, K and Ca from litter were proportional to litter mass-loss and for the Scots pine stands this meant a decreased release rate for these nutrients.