Respiration and photosynthesis of bladders and leaves of aquatic Utricularia species

In aquatic species of carnivorous Utricularia, about 10-50% of the total biomass consists of bladders. Utricularia bladders are physiologically very active organs though their chlorophyll content may greatly be reduced. To specify energetic costs of carnivory, respiration (RD) and net photosynthetic rate (PN) were compared in bladders and leaves or shoot segments of six aquatic Utricularia species with differentiated (U. ochroleuca, U. intermedia, U. floridana) or non-differentiated shoots (U. vulgaris, U. australis, U. bremii) under optimum conditions (20 degrees C, [CO2] 0.20 mM, 400 mu mol m(-2) s(-1) PAR). RD of bladders of six Utricularia species (5.1 - 8.6 mmol kg(-1) (Fw) h(-1)) was 75-200% greater, than that in leaves in carnivorous or photosynthetic shoots (1.7-6.1 mmol kg(-1) (FW) h(-1)). Within individual species, this difference was statistically significant at p < 0.002-0.01. However, PN in photosynthetic leaves/shoots (40-117 mmol kg(-1) (FW) h(-1)) exceeded that in bladders (5.2-14.7 mmol kg(-1) (FW) h(-1)) 7-10 times. RD of empty bladders of U. ochroleuca was exactly the same as that in bladders containing prey. Though Utricularia bladders are essential for uptake of growth limiting mineral nutrients N and P from prey as the main benefit of carnivory, the current results support previous work showing that bladder function requires greater metabolic (maintenance) cost and very low photosynthetic efficiency (great RD: PN ratio).