Arylsulfatase activities in soils of the Black Forest/Germany - Seasonal variation and effect of (NH₄)₂SO₄ fertilization

Arylsulfatase activities in the soil of two high-elevation sites in the Black Forest/Germany (haplic podzol Schluchsee, dystric cambisol Villingen) were determined in quarterly intervals over a period of 24 and 30 months. Both sites are forested with Norway spruce (Picea abies L. [Karst.]). Ar each study site, one untreated soil and one soil fertilized repeatedly with (NH₄)₂SO₄ (3 × 700 kg ha^-1 in 1988, 1991, and 1994) was investigated. Arylsulfatase activities generally were highest in the forest floor, medium in the mineral topsoil and lowest in the subsoil. The small-scale (< 10 m²) spatial variability of arylsulfatase activity in most cases exceeded the seasonal variation. At Schluchsee, arylsulfatase activities tended to be lower in summer and autumn than in spring, and inversely followed the seasonal fluctuation of SO₄^2- concentration in the soil seepage water. No systematic seasonal changes in soil arylsulfatase activities were observed for Villingen, where SO₄^2- concentration in soil seepage water also showed lower seasonal variation. For more than 2 years after the third fertilizer amendment in 1994, mean arylsulfatase activities in the (NH₄)₂SO₄-fertilized soils were considerably decreased compared to the untreated soils. The decreases were largest in the forest floor (-80%), but also considerable in the mineral topsoil (-70 to -80%), and in the subsoil (-45 to -60%). The decrease in soil arylsulfatase activity after fertilization lasted considerably longer than the period of elevated SO₄^2- concentration in the soil solution. This is likely to result in decreased enzymatic ester sulfate degradation, and thus may contribute substantially to the observed accumulation of ester sulfates in B horizons of the fertilized soils.