Carnivorous plants prefer to kill in broad daylight

I owe thanks to Dr Andrej Pavlovič for being a patient guinea pig with my first press-release (you can find it on Science Daily) and to Lizzie Shannon-Little at OUP for helping put it out. It’s good timing because another paper by Pavlovič on carnivorous plants and photosynthesis is now a year old – which makes it free to access.

Feeding enhances photosynthetic efficiency in the carnivorous pitcher plant Nepenthes talangensis is a good partner paper to Trap closure and prey retention in Venus flytrap (Dionaea muscipula) temporarily reduces photosynthesis and stimulates respiration. They both cover the costs of carnivory. I can see why a Venus Flytrap has a cost, there’s movement as the lobes shut on the prey, but I had expected pitcher plants to be much more passive. They just sit there don’t they?

Poisonous Pitcher plant – The Private Life of Plants – David Attenborough – BBC wildlife

It’s a fantastically sinister exhalation on the video when the traps open. It’s gratuitous monsterification of a plant, but there’s some key points in there. The trap is formed from something that you’d expect to be photosynthesising. It’s also a complex trap it requires maintenance and upkeep. That’s a cost that has to be paid for with increased respiration. It’s obviously a cost that can be paid, else plants wouldn’t eat meat, but it’s still rare for them to do so. That suggests that the costs are non-trivial so a cost-benefit analysis of pitcher plants could tell us something really useful about what the plants are doing.

Nepenthes talangensis - Pitcher plant
Nepenthes talangensis. Source: Wikipedia.

The idea for examining this, like a lot of the best ideas, was very simple. You control the light intensity, feed one sample set of pitcher plants with insect larvae and see what happens. In this case seeing what happens involved measuring the gas exchange and chlorophyll fluorescence of the plants and correlating that with nitrogen, carbon and chlorophyll concentrations, but the basic idea was elegantly simple.

The results were also very straight forward. The fed laminae showed an increase in photosynthesis compared to the unfed laminae. However, for the pitchers there was no difference in their photosynthesis regardless of whether or not they were fed. Pavlovič found that benefits of feeding greatly increased when light intensity increased too. The conclusion is that carnivory is a big advantage when in nitrogen-poor soils and sunny climes. It’s therefore no surprise to find that Nepenthes talangensis lives in nitrogen-poor soils in Sumatra.

Another finding was that only the fed plants flowered. It emphasises the importance of the pitchers in gaining nutrients for the plant.

Alas for people who like their carnivorous plants to be monsters Pavlovič’s work is bad news. You’re unlikely to wander through a dark forest fall prey to man-eating plant. There wouldn’t be enough light to make it work. Indeed anywhere dark, which is where the best monsters lurk, would be bad news for a carnivorous plant. Therefore if you want a monster plant you’d need a well-lit shop of horrors.