Tree of the Week: Exploring the underground jungle
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Why is it that we love the tree but complain so much about the roots? As if we could have one without the other. In this special edition of ‘Tree of the Week,’ Pieter Severynen sings the praises of roots, the kings of the underground jungle.
Roots and the underground jungle
What happens to trees below ground is as interesting as what we see above the surface. Trees stand up because their roots anchor them. The large perennial roots, usually oriented more horizontally than vertically, also conduct water and minerals upward and food down, and store sugars or starches manufactured by the leaves. They occur mainly in the top 18 to 30 inches of soil. Small, fairly short-lived feeder roots, less than one-sixteenth of an inch in diameter, constitute the bulk of the root mass; they grow outward and upward at a very slow pace, close to the soil surface, where they can absorb water, minerals and oxygen. These feeder roots are concentrated in the top 6 to 9 inches. Altogether the roots are bundled in the shape of a plate, which typically extends 2-3 times the width of the tree crown or more, so that an idealized tree representation looks less like a wine glass than a wine glass on a plate. Roots grow best in good soil, consisting of 50% solids, and 50% voids filled with air and water; the more compacted the soil, the more reluctant the feeder roots become to wiggle their way between the soil particles and the less the tree grows.
Utter darkness and silence may rule down below, but it is a jungle teeming with billions of creatures. Viruses, bacteria, fungi, amoebae, nematodes, arthropods and worms silently compete with, stalk, pounce on, kill and eat each other, or try to invade or take a bite out of the juicy roots. But roots have their own defenses and they do not fight alone. Millions of years ago certain beneficial fungi (mycorrhizae, fungus root) started cooperating with roots and growing on or inside them. Their thin threadlike hyphens now hugely extend the reach of roots in their search for minerals and water and help fight off competitors. In return the mycorrhizae receive sugars from the plant. The arrangement is so profitable that almost all plants use it, but in order to feed both roots and fungus a tree may have to divert below ground as much as 40% of the food produced by the leaves.
Thanks, Pieter.
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Photo Credit: Pieter Severynen