Photosynthetic CO2 affinity of the aquatic carnivorous plant Utricularia australis (Lentibulariaceae) and its investment in carnivory

Abstract

AbstractAquatic carnivorous plants usually grow in shallow dystrophic waters poor in inorganic N and P. Utricularia australis was chosen as a model plant for its prolific distribution and great ecological plasticity. The photosynthetic CO2 compensation point and factors associated with investment in carnivory and capture of prey were measured in 17 U. australis micropopulations in Třeboň basin, Czech Republic, together with water chemistry factors at these sites differing greatly in their trophic level, water hardness, and prey availability. Apical shoot growth rate was estimated at some oligotrophic sites. The micropopulations differed greatly in the proportion of traps with animal prey (2.7–70%, mean 26%), trap proportion to total biomass (1.4–42%, mean 26%), mean trap biomass (0.7–63 μg trap−1, mean 19 μg), and maximum trap size (1–3 mm, mean 2.0 mm). CO2 compensation points ranged from 0.7 to 6.1 μM (mean 2.6 μM). A weak HCO3− use (compensation point 0.51 mM) was found in plants growing in alkaline water. Trap biomass proportion did not correlate significantly with prey capture and CO2 compensation points with ambient [CO2]. A very rapid apical growth (2.5–4.2 new nodes day−1) occurred in sand pits. Thus, HCO3− use in U. australis can be induced by growing at very high pH. CO2 compensation points resembled those known in other aquatic non‐carnivorous plants. They did not reflect carnivory. In spite of very rapid apical shoot growth, the relative growth rate of U. australis can be zero in oligotrophic habitats without prey.