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Acid deposition: Effects of sulphuric acid at pH 3 on chemical and biochemical properties of bracken litter
Authors:Keith A Brown
Institution:CEGB, Central Electricity Research Laboratories, Kelvin Avenue, Leatherhead KT22 7SE, U.K.
Abstract:The effects of increased acid deposition on some biochemical and chemical properties of bracken litter overlying a podzolic soil contained in monolith lysimeters were investigated. Pairs of lysimeters each received 1500 mm yr?1 of “rain” consisting either of distilled water or pH 3.0 sulphuric acid applied evenly over a 5-yr period. The acid-treatment resulted in a marked acidification of the litter, associated with accelerated leaching of Ca2+, Mg2+, K+ and Mn2+. Acid treatment also increased the concentration of extractable Al3+ in the litter. The biochemical changes observed in the litter as a consequence of acidification included decreases of 33% in ATP content and 54% in respiration rate. Significant reductions in the mineralization rates of urea, glucose and acetate, and in the activities of 4-nitrophenylphosphatase, β-N-acetyl-d-glucosaminidase, exo-1,4,β-d-xylosidase and peroxidase were also observed in the acid-treated litter. The acid-treated litter also contained slightly less total N, ammonium-N and total P, and slightly more residual hexose carbohydrate than the control litter. The effects observed were consistent with a decrease in microbial activity associated with litter acidification and were reflected in a small (5.5%) but significant (P < 0.05) decrease in litter decomposition. Acid treatment decreased the ATP content of the mineral soil by about 13% in the 3 cm immediately beneath the litter, but below this depth no significant difference was observed.
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