Rootless aquatic plant Aldrovanda vesiculosa:: physiological polarity, mineral nutrition, and importance of carnivory

Various ecophysiological investigations are presented in Aldrovanda vesiculosa, a rootless aquatic carnivorous plant. A distinct polarity of N, P, and Ca tissue content per dry mass (DM) unit was found along Aldrovanda shoots. Due to effective re-utilization, relatively small proportions of N (10 - 13 %) and P (33 - 43 %) are probably lost with senescent leaf whorls, while there is complete loss of all Ca, K, and Mg. The total content of starch and free sugars was 26 - 47 % DM along adult shoots, with the maximum in the 7(th) - 10(th) whorls. About 30 % of the total maximum sugar content was probably lost with dead whorls. The plant was found to take up 5 - 7 times more NH4+ to NO3- from a mineral medium. Under nearly-natural conditions in an outdoor cultivation container, catching of prey led to significantly more rapid growth than in unfed plants. DM of the fed controls was 48 % higher than in the unfed plants. The controls produced 0.69 branches per plant, while the unfed plants did not produce any. However, the N and P content per DM unit increased by 6 - 25 % in the apices and the first 6 whorls in the unfed variant, as compared to the fed controls. It may be suggested that carnivory is very important for Aldrovanda.