The influence of prey capture on photosynthetic rate in two aquatic carnivorous plant species

Photosynthetic (PN) and dark respiration rate (RD) were measured in two species of aquatic carnivorous plants, Aldrovanda vesiculosa and Utricularia australis, growing with or without prey in an outdoor growth experiment. After 7–14 days, the positive growth effect of feeding on prey (apical growth rate, plant size, branching) was evident in both species. Tissue N content in young leaf whorls of both species fed on prey was significantly lower (by 54% in Aldrovanda, by 86% in Utricularia) than that in unfed variants, while tissue P content was about the same. In both species, chlorophyll a content was consistent with tissue N content and RD in fed and unfed variants was very similar. However, PN was significantly greater in fed plants of Aldrovanda, while lower in Utricularia. It is possible to conclude that feeding on prey in aquatic carnivorous plants leads to neither an increase of shoot tissue N content nor PN per unit biomass. Thus, the main physiological effect of catching prey is not enhancement of PN, but to provide N and P for essential growth processes in juvenile tissues.