By which mechanism does prey capture enhance plant growth in aquatic carnivorous plants: Stimulation of shoot apex?

Prey capture in rootless aquatic carnivorous plants usually leads to more rapid plant growth, especially to increasing apical shoot growth rate and branching. Yet, the mechanism of this growth effect is still unknown. In this paper, dark respiration (R(D)) and tissue N and P content were estimated in young parts of shoot apices in three aquatic carnivorous plants, Aldrovanda vesiculosa, Utricularia australis, and U. bremii, grown with or without prey in a 12-d greenhouse growth experiment. Fed plants of all three species were significantly longer and had more mature leaf nodes on the main shoot than unfed plants. Similarly, the apical shoot growth rate of fed plants in all three species was significantly higher by 49-85% than that of the unfed variants (day 6-12) and so also was shoot branching. In A. vesiculosa only, tissue N content both in apices and shoot segments of fed plants was significantly greater that in unfed plants. Both apical and shoot P content was significantly greater in fed plants of A. vesiculosa and U. australis, while the P contents were the same in U. bremii. Feeding on prey significantly increased R(D), of shoot apices in A. vesiculosa, while the values for fed and tided plants were exactly the same in the other two species. In conclusion, the more rapid growth due to feeding could hypothetically be caused by stimulating the cell division in the youngest parts of shoot apex due to a faster allocation of prey-derived N and P. The methods used in this study were not sensitive enough to prove this hypothesis although the results partly support it.