Some species of carnivorous houseplants, Nepentheshave switched from catching and digesting insects to absorbing animal feces for their daily dose of nutrients—and it’s a switch that’s proving very beneficial.
These botanical faeces eaters manage to take in more nitrogen through their diet than others Nepenthes that snack on prey, the researchers found. The difference is significant, even if the new food regimen doesn’t sound so appetizing.
There are some important lessons here in terms of how plants can adapt and evolve to cope with environmental challenges: by understanding more about the way Nepenthes have improved their nutritional intake, we can better protect them.
“A handful of Nepenthes species have evolved away from carnivory to a diet of animals, says Alastair Robinson, a botanist from the Royal Botanic Gardens Victoria in Australia.
“We found that nitrogen capture is more than twice as great in species that capture mammalian excrement than in others Nepenthes.”
The team looked at six species and four hybrids of Nepenthes in Malaysian Borneo, analyzed tissue samples to look at the amount of nitrogen and carbon that had been captured from outside the plants.
Nitrogen is a key driver of photosynthesis and other plant processes, and the researchers found that the heavier 15N isotope of nitrogen was significantly more abundant in Nepenthes compared to nearby non-carnivorous plants, and especially in the species that specialized in consuming mammal droppings.
Being carnivorous helps plants to take in important nutrients they would otherwise not get from nitrogen-poor soil. With reductions in insect populations at higher elevations, some plants appear to be turning to alternative sources for the element.
“Insect prey are scarce at tropical summits above 2,200 meters (7,218 feet), so these plants maximize nutritional returns by collecting and retaining fewer, higher-value nitrogen sources such as tree tip dung,” says Robinson.
In most Nepenthes species, foraging insects slip on the smooth surfaces and edges of “pot” leaves and fall into a trap of water and digestive fluids. As discovered in 2009, some of the plants have developed a mutually beneficial relationship with mountain wood mice: the animals deposit nitrogen-rich waste in the pitchers while they feed on carbohydrates on the plant lids.
Further research revealed a similar relationship between certain Nepenthes species and top rats, birds and bats. Now we know that this resource trade with animals is more beneficial in terms of food capture than catching insects.
All this new understanding can play into conservation efforts. There is more Nepenthes species at risk than any other carnivorous plant genus, with 40 percent of species labeled as critically endangered, threatened or currently vulnerable.
“Understanding the ecological requirements of species, particularly where species are involved in complex biological mutualisms, is critical in conservation planning and management for endangered carnivorous plants,” the researchers write in their published paper.
The research is published in Annals of Botany.