Nepenthes pitchers are CO₂-enriched cavities, emit CO₂ to attract preys

Carnivorous plants of the genus Nepenthes supplement their nutrient deficiency by capturing arthropods or by mutualistic interactions, through their leaf-evolved biological traps (pitchers). Though there are numerous studies on these traps, mostly on their prey capture mechanisms, the gas composition inside them remains unknown. Here we show that, Nepenthes unopened pitchers are CO₂-enriched 'cavities', when open they emit CO₂, and the CO₂ gradient around open pitchers acts as a cue attracting preys towards them. CO₂ contents in near mature, unopened Nepenthes pitchers were in the range 2500-5000 ppm. Gas collected from inside open N. khasiana pitchers showed CO₂ at 476.75 ± 59.83 ppm. CO₂-enriched air-streaming through N. khasiana pitchers (at 619.83 ± 4.53 ppm) attracted (captured) substantially higher number of aerial preys compared to air-streamed pitchers (CO₂ at 412.76 ± 4.51 ppm). High levels of CO₂ dissolved in acidic Nepenthes pitcher fluids were also detected. We demonstrate respiration as the source of elevated CO₂ within Nepenthes pitchers. Most unique features of Nepenthes pitchers, viz., high growth rate, enhanced carbohydrate levels, declined protein levels, low photosynthetic capacity, high respiration rate and evolved stomata, are influenced by the CO₂-enriched environment within them.