   Know Your Roots - July 18, 2001 Jeff Schalau, County Director, Agent, Agriculture & Natural Resources Arizona Cooperative Extension, Yavapai County Every once in a while, I feel the need to infuse some basic biology into this column. I believe this helps people understand how plants grow thereby increasing their skills in caring for their gardens and landscapes. This week's topic is plant roots: how they function and why they are important. The word "root" has meanings and uses in the English language. "Root" not only refers to an underground portion of a plant, but also has meanings in the disciplines of music, mathematics, anthropology, and even dentistry. In all cases, "root" refers to a basis or origin. In plants, roots anchor the plant, absorb and conduct water and nutrients from the soil to other plant parts, and, in many cases, store energy for later use by the plant. Germinating seeds have a primary root that grows downward into the soil. On young roots, new cells are formed at the root tip. On the very end of the new root is a thimble-shaped cluster of cells called a root cap. The root cap is actually a sacrificial structure that helps the root penetrate through the soil. As the root grows downward, the root cap cells are sloughed off creating a slimy surface that lubricates the root as it goes deeper. Just behind the root cap is a growing point called the apical meristem, which produces new root cells and a new root cap to replace the sloughed off cells. The root cells elongate pushing the root tip deeper into the soil. After the root tip has passed through a region of soil, the new root begins to mature producing root hairs. Root hairs are relatively short-lived and form after the root cells have elongated. Root hairs are very important to gardeners because they are the primary surfaces that absorb water and mineral nutrients from the soil. The newly forming roots with their root cap, root tip, zone of elongation, and root hairs make up what gardeners often call "feeder roots". When transplanting, it is important to retain as many feeder roots as possible to ensure proper uptake of water and nutrients and allow quick recover from this disturbance. Conversely, if a plant is torn from the soil, many feeder roots will be left behind decreasing the probability of survival. As plants mature, roots branch and expand their zone of soil contact forming a root system. In general, plants have one of two different types of root systems. Conifers and their relatives (gymnosperms) and broadleaved plants (dicotyledons) both have a taproot that grows downward usually branching along the way. Grasses and their relatives (monocotyledons) produce fibrous root systems that radiate out into the soil from the base of the plant. Taproots are often deeper, fleshier or woody, long-lived, and have more branching. Fibrous roots tend to be smaller, shorter-lived, and branch less. When thinking of a taproot, a carrot may come to mind. While a carrot is an example of a taproot, don't think that mature woody plants and trees have a large carrot-like structure below ground. They usually don't. Instead they have a highly branched, complex network of woody conducting tissue to anchor the plant and conduct water an nutrients. Feeder roots are found near the soil surface (3 to 5 inches deep). In irrigated landscape situations, mature tree root systems are often not deeper than 5 or 6 feet with the bulk of the root system being less than 3 feet deep. However, these root systems may spread laterally 3 to 5 times the width of the crown. Now that I have made sweeping generalizations about the depth of woody plant roots in landscapes, I know from experience what some of you are probably thinking. Yes, roots can also go very deep. There was a live mesquite root found 175 ft deep in a mine in southern Arizona. What was it doing there? I have no idea, but that is the world record. I do know that roots do not seek out water and nutrients. They randomly explore the underground environment and proliferate where resources are abundant. This is most often realized near broken sewer lines and leach fields. Grass root systems are often under appreciated. Grasses with their fibrous root systems are excellent at holding soil in place to reduce erosion. Perennial grasses that are planted in lawns and dot the native landscape also contribute organic matter to the soil. Each year, old roots die and new roots are formed. The dead roots decay, are attacked by beneficial soil organisms (bacteria, fungi, protozoa, worms, and insects) releasing nutrients and producing organic matter. This turnover of roots is what contributes to the dark, rich soils found in some grass-dominated landscapes. On the practical side, learn to visualize the root system that is present on each plant species you grow in your garden and landscape. At then of the growing season, pull up a few plants and look at branching patterns. Compare annuals to perennials to woody plants. Learn to apply water and nutrients where they are needed not simply where it is convenient. If you installed drip irrigation to establish trees and shrubs, consider where the feeder roots will be 5 or 10 years down the road and adjust accordingly. These are just a few ways that your garden will benefit from your better understanding of root systems. The University of Arizona Cooperative Extension has publications and information on gardening and plant selection. If you have other gardening questions, call the Master Gardener line in the Cottonwood office at 646-9113 or E-mail us at mgardener@kachina.net and be sure to include your address and phone number. Find past Backyard Gardener columns or submit column ideas at the Backyard Gardener web site: http://ag.arizona.edu/yavapai/anr/hort/byg/. |