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Purple pitcher plants and peat bogs

7 min read / May 22, 2018 / By Allaire Diamond

Discover a mysterious ecosystem home to a beautiful carnivorous plant

Ancient bogs can be dozens of feet deep

Entering a peat bog, I have the distinct sense of encountering a different world. Expanses of sphagnum moss form a subtly diverse carpet traced by delicate, arching stems of small cranberry and creeping snowberry, studded with glossy berries and pale brown mushrooms. Woody copses of bog rosemary and leatherleaf rise above the moss, and white puffs of cottongrass float on fine waving stems.

Many of Vermont’s bogs form in kettles, isolated depressions that were formed by chunks of melting glacial ice. Disconnected from local watersheds, kettles receive nearly all of their water from rain and snow. With virtually no inflow or outflow of water, kettles soon become low-oxygen environments; plant matter cannot decompose, but rather accumulates over time. The springy mat of a bog’s surface is actually a few millennia of biological remains that may be several dozen feet deep!

Bogs inspire creativity

The nutrient-poor bog forces plants to get creative, perhaps none more so than the purple pitcher plant, Sarracenia purpurea. Its dramatic, specialized leaves form multicolored ‘pitchers’ that fill with rain and snow, hosting tiny self-contained ecosystems—like the bogs themselves.

Downward-pointing hairs guide insects into the pitcher, where they drown and are dismembered by the resident community of microorganisms. Larvae of the pitcher plant midge and the pitcher plant flesh fly—insects found only in pitchers—use powerful jaws to break drowned insects into food for protozoans and tiny animals called rotifers. Bacteria complete the job, decomposing bits of bugs into minerals and nutrients, some of which are taken up by the plant itself.

Pitcher plants rely on the creatures in their pitchers for about 10 percent of their nitrogen needs. As they photosynthesize, they release oxygen back into the water, keeping it habitable for their motley crews of predators, prey, and decomposers.

Pitcher plants can quickly adapt to new conditions

Scientists have long studied pitcher plants, not only to learn their unique biology, but also as model ecosystems that could demonstrate how larger systems, like ponds and lakes, might respond to environmental change.

After researchers in Massachusetts added high amounts of ground-up wasps to pitchers, oxygen levels decreased and conditions in the pitcher reached a ‘tipping point’ where the complex food web couldn’t function. This led to a buildup of dead bugs with no one to break them down, leading to even less available oxygen and the spiraling effects of an ecosystem out of whack. The researchers likened this process to the conditions that create an algae bloom when excess nutrients enter a lake.

How does the pitcher plant respond? Another study found that with more available nitrogen, such as that resulting from industrial and agricultural pollution, pitcher plants will simply begin to produce leaves specialized for photosynthesis rather than hosting a miniature ecosystem. The plant can adapt to higher levels of nitrogen deposition, but the creatures that rely on it might need to find new digs.

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