| An experiment comparing effects of sulphuric acid and reduced N deposition on
soil water quality and on chemical and physical growth indicators for forest ecosystems
is described. Six H2SO4 and
(NH4)2SO4 treatment loads, from 0 – 44 and
0 – 25 kmolc ha-1 yr-1,
respectively, were applied to outdoor microcosms of Pinus sylvestris seedlings in 3 acid
to intermediate upland soils (calc-silicate, quartzite and granite) for 2 years. Different
soil types responded similarly to H2SO4 loads, resulting in decreased
leachate pH, but differently to reduced N inputs. In microcosms of calc-silicate soil,
nitrification of NH4 resulted in lower pH and higher cation leaching than in
acid treatments. By contrast, in quartzite and granite soils,
(NH4)2SO4 promoted direct cation leaching, although
leachate pH increased. The results highlighted the importance of soil composition on the
nature of the cations leached, the SO4 adsorption capacities and microbial N
transformations. Greater seedling growth on calc-silicate soils under both treatment types
was related to sustained nutrient availability. Reductions in foliar P and Mg with higher
N treatments were observed for seedlings in the calc-silicate soil. There were few
treatment effects on quartzite and granite microcosm tree seedlings since P limitation
precluded seedling growth responses to treatments. Hence, any benefits of N deposition
to seedlings on quartzite and granite soils appeared limited by availability of
co-nutrients, exacerbated by rapid depletion of soil exchangeable base cations.
Keywords: acidification, manipulation, nitrogen, ammonium, deposition, soil, drainage,
pine, microcosms, forest |