Effects of simulated acid precipitation on the cycling of manganese under Sitka spruce ( Picea sitchensis )

Abstract

Simulated acid rain at pH 3.3, 4.3 and 5.3 has been applied by overheadspraying to reconstructed soil profiles and young Sitka spruce (Piceasitchensis) trees in pots to assess the effect of rainfall acidityonthe fate and recycling efficiency of Mn from 54Mn-labelled Sitkaspruce litter. The concentration of 54Mn in throughfall wassignificantly increased by acidification of the rain, but 54Mnactivity in drainage water remained low and was not significantly affected. Thefact that only < 1.5% of 54Mn was lost in drainage water suggeststhat forest ecosystems efficiently retain Mn, at least in the short term. Thebulk of 54Mn (approximately 60 to 70%) was retained in the litterlayer. Compared with rain at pH 4.3, rain at pH 3.3 acidified L/F and H/Ahorizon soils. The amount of 54Mn found in the different soilhorizons was only influenced significantly by rainfall acidity in the E horizonsoil, however, where 54Mn activity was increased by the most acidtreatment. The activity of 54Mn in Sitka spruce needles did notdiffer significantly with treatments.