Phosphorous plays important roles in vital functions of all organisms as a macronutrient. Quantitatively, the amount of plant P uptake can be compared to nitrogen and potassium. Phosphorous can be found in soils in both inorganic and organic forms however, plants can uptake inorganic forms exclusively. Therefore, the organic reservoirs of P in soil can only be participating in plant nutrition via P mineralization. The P mineralization processes in soils are an enzyme mediated procedure which is mainly catalyzed by acid and alkaline phosphomonoesterases. The objective of this study were to identify i) the soil physical, chemical, biochemical and biological factors influence the activity of acid and alkaline phosphatase ii) the differences between the patterns of acid and alkaline phosphatase distribution in calcareous soils. For these purposes 22 calcareous soils were collected from Isfahan, Chaharmahal va Bakhtiari, Tehran, Ghazvin and Gilan provinces. Some soil physicochemical properties including soil particle size distribution, soil organic C concentration, calcium carbonate equivalent, electrical conductivity (EC) and pH were measured. The activity of acid and alkaline phosphatase, urease, L-asparaginase and L-glutaminase were assayed. Soil microbial biomass and soil biological activity indices including L-arginine ammonification and soil basal respiration were also measured. Soil biological pools of N such as inorganic N concentration, soluble organic N, aerobic and anaerobic N mineralization were determined. Alkaline phosphatase was significantly correlated with soil organic C (0.93***). Similar results was observed for acid phosphatase (0.68***). It was observed that the degree of association between alkaline phosphatase and soil organic C was greater than that of acid phosphatase. The degree of association between alkaline phosphatase and L-asparaginase, L-glutaminase and urease was consistently greater than that of acid phosphatase. Similar results were observed for L-arginine ammonification. Soil basal respiration was also correlated with both alkaline and acid phosphatase whereas; the degree of correlation was greater for alkaline phosphatase. Indices of soil N bioavailability were also correlated with both alkaline and acid phosphatase however, the degree of association ware dissimilar. It was suggested that soil alkaline phosphatase and acid phosphatase are originated from different sources. Soil alkaline phosphatase is mostly form microbial sources while soil acid phosphatase is mostly from plant root origin. In the current study we demonstrated that the pattern of association between alkaline phosphatase and soil physicochemical and biological characteristics are pretty similar with those of acid phosphatase however, the degree of association is quite different. The degree of association between alkaline phosphatase and soil physicochemical and biological properties is consistently greater than that of the acid phosphatase. This finding is in agreement with the different origins of the two soil enzymes. The enzyme with different sources behave differently because the soil enzyme origin can influence the stability and location of the enzyme in soil and that it may influence the association of the enzyme with other soil properties. Keywords : Alkalin phosphatase, Acid phosphatase, Urease, L-asparaginase, L-glutaminase, Argenin ammonification, Microbial basal respiration, N mineralization.
