Effects of phosphorus addition and energy supply on acid phosphatase production and activity in soils

Abstract

To find out how acid phosphatase activity and production in some Alberta soils may be related to soil properties and past fertilizer history, soils of varying organic matter content, extractable P and P fertilization history were assayed for acid phosphatase using p-nitrophenyl phosphate as substrate. The effect of solution P concentration during the phosphatase assay was examined. The effect of P on the production of new phosphatase was examined in soils incubated with an added energy supply or orthophosphate. Phosphatase activity was influenced by P fertilization practices during the 5 yr before sampling. In a Black Chernozemic soil (Malmo SiCL) with a high organic matter content and high initial phosphatase activity, P fertilization at 27 or 54 kg P ha −1 y −1 for 5 yr reduced phosphatase activity by about 20%. However, in a Grey Luvisolic soil (Cooking Lake L) with low organic matter and initial phosphatase, P fertilization at 54 kg P ha −1y −1 for 5 yr tended to increase activity, probably by increasing plant root growth and organic matter additions. Assay solutions containing orthophosphate at 0.55 mM reduced activity by 25% and 47% in a Malmo SiCL and Maleb L (Orthic Brown Chernozem) soil respectively. Further increases of phosphate concentration to 5.5 mM reduced phosphatase activity by 50% and 76% in the Malmo and Maleb L soils respectively. Phosphatase activity was increased up to 6-fold by incubation of soil with glucose and NH 4NO 3. Addition of P to produce an added C: added P ratio of 20:1 completely prevented synthesis of phosphatase by proliferating organisms and had a slight inhibitory effect on phosphatase already present. Similarly, addition of P without C in a 6-week incubation had only a small effect on phosphatase activity and maintained P concentrations in the assay solutions slightly below 0.55 mM. It was concluded that the effect of phosphate on soil phosphatase operates more through its effect on phosphatase synthesis than on activity of existing phosphatase.