Saturday, July 21, 2012

Partnerships in Light and Dark

Breaking out of the dense canopy onto a rocky cliff, I glance first at the stunning view of Lake Superior, then to the shrubs around my feet. Deep blue is the color of the day. This section of the Superior Hiking Trail is known as “Blueberry Ridge,” and not without cause. Blueberries can survive in this hot sun and poor soil where many plants cannot, and in fact, this is where blueberries thrive. We saw blueberry plants in the deeply shaded forest – but not a single berry. Now, with the morning sun in our eyes, we pick steadily from clusters of wild candy.

Blueberry plants are sugar factories. They capture the plentiful sunlight energy and use it to manufacture fructose from water and carbon dioxide. But neither a plant nor a six-year old (or a berry-picking naturalist) can live on sugar alone, try as they might. In this thin, rocky soil, getting the right suite of nutrients and water for growth can be tough. The blueberry plants have helpers, though, just like many other plants in their Heath Family.

If you, or a plant biologist, were to stain a blueberry root with dye and view it through a microscope, you would see thin strands of fungal hyphae coiled within the root cells and extending in thin threads outside the root. The hyphae act like root-extensions, drawing in nutrients and water beyond the typical reach of the blueberry. The fungus, a decomposer, can break down soil components to access nutrients that are otherwise locked away. The blueberry pays for this service by giving the fungus little sugar snacks.

The blueberry’s mycorrhizal (fungus-root) relationship is wholesome compared to some of its close kin. Those shady cousins have a more deceitful way to make a living.

Back in the forest, layer upon layer of leaves filter out most of the noontime light before it reaches the forest floor. Red-capped Russula mushrooms with white stalks brighten up the brown leaf litter. The few understory species that can survive here must have low energy needs, and an ability to take advantage of sun whenever they catch a fleeting glimmer. Or they might be theives.

While your stereotypical burglar dresses in all black, one bandit shines with the translucent white glow of innocence. Sometimes called Indian pipe, ghost plant, or corpse plant, the cluster of eight-inch tall flower stalks is actually a cousin of blueberries and cranberries that takes the mycorrhizal relationship to the extreme. Indian pipe has no chlorophyll to make it green, and therefore cannot carry out photosynthesis. It does not need to make food, because this myco-parasitic plant is getting ALL of its food from a fungus.

It just so happens that some of the most common fungal providers for Indian pipe are Russulas, those pretty red mushrooms that are popping up everywhere right now. These fungi are engaged in their own mycorrhizal relationship with the trees, and are currently exchanging micro-nutrients and water for the sweet products of photosynthesis. Indian pipe fools the fungus into “thinking” they are forming a mycorrhizal relationship. Then it steals the sugars, giving nothing in return. Scientists have traced the one-way flow of sugars by introducing radioactive carbon into tree leaves, watching it flow down through the Russula, and out into the Indian pipe, where it stays.

In both sunlight and shadow, the intricate relationships of nature fill our lives with sweetness and beauty.

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