Persistence of catalytic activity of fungal phosphatases incubated in tropical soils

Catalytic activity of extracellular enzymes in soil controls many biogeochemical cycles. The efficiency of extracellular enzymes depends on their interaction with soil organo-mineral surfaces and their resistance to degradation and inactivation. Little is known about the factors that control the time dependence of enzyme activity in soil. We have monitored catalytic activity of native and added phosphatase incubated for up to one month in moist soil. Two fungal phosphatases and three tropical soils (two acrisols with contrasting organic matter content and a vertisol) were compared and the effect of soil sterilisation measured. The enzymes had different stabilities in solution. Activity of Hebeloma cylindrosporum phosphatase was protected in acrisols, but not in contact with the vertisol. In contrast, the decline of activity of Suillus collinitus phosphatase followed the same trend in solution and in the presence of each of the soils. Sterilisation decreased native phosphatase activity. The rate of decline of added phosphatase activity was identical in sterile and non-sterile soils. We discuss the effects of degradation of the enzyme in soil and changing relative activity in the adsorbed state. ► Activity of two fungal phosphatases declined differently in solution. ► Protection of catalytic activity of adsorbed enzyme is not always observed. ► Native soil phosphatase activity was constant during one-month incubation. ► Sterilization decreased native phosphatase activity. ► Degradation and changing activity in the adsorbed state may contribute to decline.