In: Phyton 55, Fasc. 1 (2015): S. 131-148 DOI: 10.12905/0380.phyton55(1)2015-0131

Regulation of the Investment in Carnivory in Three Aquatic Utricularia Species: CO2 or Prey Availability?
Key words: Aquatic carnivorous plants, bladderworts, Utricularia vulgaris, U. australis, U. reflexa, growth experiment, CO2 or prey addition, foliar N and P content.

Adamec L. 2015. Regulation of the investment in carnivory in three aquatic Utricularia species: CO2 or prey availability? – Phyton (Horn, Austria) 55 (1): 131 – 148.

Summary

The structural investment in carnivory (IIC) as a relative proportion of trap biomass (DW) was investigated in three aquatic Utricularia species (U. vulgaris, U. australis and U. reflexa) in a 12–14 d greenhouse growth experiment. The two-factorial experiment included the presence or absence of prey (zooplankton) for a high (0.30-0.58 mM) or low (0.024-0.062 mM) CO2 concentration in the culture water. Various plant growth parameters, including traps and foliar N and P contents in young shoot segments, were estimated. All species with either CO2 or prey addition had significantly more mature leaf nodes on the main shoots, were more branched and their apical shoot growth was more rapid than the -CO2 or -Prey variants. The mean trap DW increased greatly (2.7-249 times) due to CO2 addition, while the effect of prey addition was much less and rather ambiguous. Both CO2 and prey addition significantly influenced the trap number per mg leaf node only in U. vulgaris. Thus, trap DW rather than the number of traps per leaf DW, is the basis for an ecological regulation of the IIC in aquatic Utricularia. CO2 addition markedly increased the IIC in all species, while the effect of prey addition was much less. The IIC in all species correlated significantly and negatively with shoot N and P contents but highly significantly and positively with the mean trap DW. Generally, under a surplus CO2 and favourable light conditions, the trap production as the IIC in aquatic Utricularia is supported by prey capture more (positive feedback) than the apical shoot growth, but the IIC apparently does not depend on the very low shoot N or P content. At medium CO2 concentration, shoot N and P contents are very variable and regulate the IIC by negative feedback (“nutrient” regulation). Under poor photosynthetic conditions, however, the trap production is blocked by a shortage of photosynthates, which are allocated preferentially to shoot apices and branching, but probably also by the very high shoot N and P content. The regulation of trap production in Utricularia therefore includes two components. High CO2 concentration as the crucial prerequisite for high photosynthetic rate (“photosynthetic” regulation) is superior to the negative feedback regulation by tissue N or P content in young shoot segments.