Enzymatic activities in traps of four aquatic species of the carnivorous genus Utricularia.

•   Here, enzymatic activity of five hydrolases was measured fluorometrically in the fluid collected from traps of four aquatic Utricularia species and in the water in which the plants were cultured. •   In empty traps, the highest activity was always exhibited by phosphatases (6.1-29.8 µmol l-1  h-1 ) and β-glucosidases (1.35-2.95 µmol l-1  h-1 ), while the activities of α-glucosidases, β-hexosaminidases and aminopeptidases were usually lower by one or two orders of magnitude. Two days after addition of prey (Chydorus sp.), all enzymatic activities in the traps noticeably decreased in Utricularia foliosa and U. australis but markedly increased in Utricularia vulgaris. •   Phosphatase activity in the empty traps was 2-18 times higher than that in the culture water at the same pH of 4.7, but activities of the other trap enzymes were usually higher in the water. Correlative analyses did not show any clear relationship between these activities. •   Trap comensals (Euglena) could be partly responsible for production of some trap enzymes. The traps can produce phosphatases independently of catching prey. Taking into account the enzymatic activities in traps, phosphorus uptake from prey might be more important than that of nitrogen for the plants.