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Pitcher Plant’s Web of Life

July 20, 2010

Find yourself a sphagnum covered bog in New England and you’re sure to find a pitcher plant. But peer a little closer and you’ll find a whole self-contained world within it.

Northern pitcher plants (Sarracenia purpurea) grow as a rosette and produce 6 to 12 new tubular leaves each season. A bunch of pitchers next to each other belong to the same individual. The leaves open every few weeks and the “pitcher” that is formed fills with rainwater. Leaves capture the sun for photosynthesis during their first year, but as they age they are used by the plant to capture prey for 1 to 2 years before they fall apart. The small prey die and break down in the pitcher. The plant absorbs nutrients from the prey that are not available from the acidic bog.

The prey are attracted to the pitcher by a sugar secretion on the lip of pitchers, as well as color and scent. Because of a waxy, slippery coating on the lip of the pitcher, they sometimes fall into the water inside the pitcher and find it difficult to climb out because of very fine, downward-angled hairs on the walls of the leaf.

Nicholas Gotelli from the University of Vermont and Aaron Ellison from Harvard have begun to study the effects of increased inputs of atmospheric nitrogen from acid precipitation. They have discovered that as more nitrogen is added to bogs the pitcher plants shift from producing water-filled pitcher-shaped leaves to flat leaves that are used for photosynthesis. This is an amazingly fast morphological change.

There is a complex web of life living within each pitcher. The base of the food web is comprised of captured prey, mostly ants and flies. These are shredded and partially consumed by Pitcher Plant Midge (Metriocnemus knabi) and Pitcher Plant Fly (Fletcherimyia fletcheri) larvae. Shredded prey are processed by a host of bacteria and protozoa. These are in turn prey to a filter-feeding rotifer (Habrotrocha rosi) and a mite (Sarraceniopus gibsonii). Larvae of the Pitcher Plant Mosquito (Wyeomyia smithii) feed on bacteria, protozoa, and rotifers. Older mosquito larvae (third instar) eat rotifers and smaller mosquito larvae (first and second instar).

Gotelli and Ellison found that the web of life extends outside of the pitcher too. The leaves exude a sugar that attracts ants. Some ants forage successfully while a few fall into the pitcher. Two moths, the Pitcher Plant Moth (Exyra fax) and The Pitcher Plant Borer (Papaipema appassionata), only use the Pitcher Plant as a host plant for their caterpillars to feed and grow. The larvae of the Pitcher Plant Moth can drain and kill individual pitchers. The Pitcher Plant Borer feeds on the roots and can sometimes kill the entire plant. Repeated or heavy feeding by the moth larvae reduces the amount of available sugar to the ants.

Check out the hidden world of the Pitcher Plant the next time you are on a boardwalk though a bog.

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