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Biochemical and mesophyll diffusional limits to photosynthesis are determined by prey and root nutrient uptake in the carnivorous pitcher plant Nepenthes x ventrata.

BACKGROUND AND AIMS
Carnivorous plants can enhance photosynthetic efficiency in response to prey nutrient uptake but the underlying mechanisms of increased photosynthesis are largely unknown. Here we investigated photosynthesis in the pitcher plant Nepenthes x ventrata in response to different prey-derived and root mineral nutrition to reveal photosynthetic constrains.


METHODS
Nutrient-stressed plants were irrigated with full inorganic solution or fed with four different insects: wasps, ants, beetles and flies. Full dissection of photosynthetic traits was achieved by means of gas exchange, chlorophyll fluorescence and immunodetection of photosynthesis-related proteins. Leaf biochemical and anatomical parameters together with mineral composition, N and C isotopic discrimination of leaves and insects were also analysed.


KEY RESULTS
Mesophyll diffusion was the major photosynthetic limitation for nutrient-stressed Nepenthes x ventrata, while biochemistry was the major photosynthetic constriction after nutrient application. The better nutrient status of insect-fed and root-fertilized treatments increased chlorophyll, pigment-protein complexes and Rubisco content. As a result, both photochemical and carboxylation potential were enhanced, increasing carbon assimilation. Different nutrient application affected growth development, and root-fertilized treatment invested more biomass in leaves instead of pitchers.


CONCLUSIONS
The study resolved a 35 year old hypothesis proposed by Givnish et al. (1984) that carnivorous plants increase photosynthetic assimilation via the investment of prey-derived nitrogen to photosynthetic apparatus. The equilibrium between biochemical and mesophyll limitations of photosynthesis is strongly affected by the nutrition treatment.