Effect of artificial irrigation,acid precipitation and liming on the microbial activity in soil of a spruce forest

Summary The effects of irrigation, acid precipitation and liming on the bioactivity in a spruce forest soil were measured with different tests. Except for the iron reduction test and the FDA hydrolysis, the highest activities were measured in the upper horizons and mostly decreased gradually in the deeper ones. The determination of heat output and respiration without additional energy supply and ATP measurement gave similar results: acid precipitation inhibits the bioactivity in O₁ and O_f1, layers; lime stimulated it mostly in O_f2 horizons. Except for the results of ATP measurement, in O_f2 horizons the influence of lime exceeded that of acid irrigation. The results obtained from respiration and microcalorimetric measurements after the introduction of an energy supply were similar: Humidity, derived either from acid precipitation or from irrigation, stimulated the activity as well as lime, clearly in O_f2, to a smaller extent also in deeper horizons. The bioactivity in Oft increased significantly in the plots in the order: control, plot with acid irrigation, plot with normal irrigation, limed plot, limed plot with acid irrigation, and limed plot with normal irrigation. The difference between irrigated and acid-irrigated plots is due to the inhibitive effects of protons and SO ₄ ^2– . The FDA hydrolysis test showed a clear stimulative effect of humidity in O_f horizons of non-limed plots. With the iron reduction test, stimulation in acid-irrigated and inhibition in limed samples was demonstrated. The maximum bioactivity measured with this method was localized in deeper horizons.