Feeding enhances photosynthetic efficiency in the carnivorous pitcher plant Nepenthes talangensis

BACKGROUND AND AIMS: Cost-benefit models predict that carnivory can increase the rate of photosynthesis (AN) by leaves of carnivorous plants as a result of increased nitrogen absorption from prey. However, the cost of carnivory includes decreased AN and increased respiration rates (RD) of trapping organs. The principal aim of the present study was to assess the costs and benefits of carnivory in the pitcher plant Nepenthes talangensis, leaves of which are composed of a lamina and a pitcher trap, in response to feeding with beetle larvae. METHODS: Pitchers of Nepenthes grown at 200 μmol m⁻² s⁻¹ photosynthetically active radiation (PAR) were fed with insect larvae for 2 months, and the effects on the photosynthetic processes were then assessed by simultaneous measurements of gas exchange and chlorophyll fluorescence of laminae and pitchers, which were correlated with nitrogen, carbon and total chlorophyll concentrations. KEY RESULTS: AN and maximum (Fv/Fm) and effective quantum yield of photosystem II (ΦPSII) were greater in the fed than unfed laminae but not in the fed compared with unfed pitchers. Respiration rate was not significantly affected in fed compared with unfed plants. The unfed plants had greater non-photochemical quenching (NPQ) of chlorophyll fluorescence. Higher NPQ in unfed lamina did not compensate for their lower ΦPSII, resulting in lower photochemical quenching (QP) and thus higher excitation pressure on PSII. Biomass and nitrogen and chlorophyll concentration also increased as a result of feeding. The cost of carnivory was shown by lower AN and ΦPSII in pitchers than in laminae, but RD depended on whether it was expressed on a dry weight or a surface area basis. Correlation between nitrogen and AN in the pitchers was not found. Cost-benefit analysis showed a large beneficial effect on photosynthesis from feeding as light intensity increased from 200 to 1000 μmol m⁻² s⁻¹ PAR after which it did not increase further. All fed plants began to flower. CONCLUSION: Feeding pitchers with insect larvae increases AN of leaf laminae, due to higher nutrient acquisition, with strong correlation with nitrogen concentration, but AN of pitchers does not increase, despite increased nitrogen concentration in their tissue. Increased AN improves growth and reproduction and is likely to increase the competitive advantage of carnivorous over non-carnivorous plants in nutrient-poor habitats.