Getting to the Root of the Problem

As a Community Manager you’ve probably seen the power of roots.  You’ve seen roots getting under sidewalks lifting them up into the air.  You’ve seen roots getting into buildings causing slab damage and even lifted slabs.  You’ve seen roots destroying the asphalt in streets.  You’ve seen roots getting into all type and manner of pipes and literally ripping them apart.

Have you ever wondered how in the world that these seemingly innocuous tree roots can wield such power?  Recently a San Diego Union Tribune article written by Sherri Seethaler, set the record straight about these denizens of the soil.  “Heaved sidewalks, punctured pipes, not to mention botanically themed horror flicks, make it easy to imagine roots as unyielding battering rams.  Yet the ability to penetrate hard-packed soil and other barriers owes much to roots’ exquisite sensitivity to their environment.

Roots detect and integrate a cacophony of signals about environmental factors, including gravity, moisture, light, nutrients, temperature, carbon dioxide, oxygen, bacteria, fungi and texture.  When the tip of a growing root encounters a combination of desirable and undesirable signals, it responds in a hierarchical manner.

For example, exposure to a toxic level of metal ions can prompt a root to defy gravity and thrust itself into the air.  Environmental signals lead to complex chemical conversations within root tips.  The conversations involve proteins, ions, pH changes and plant hormones; and ultimately tell the root tip which direction to turn.

In a bout between tree versus sidewalk, roots seem to use their super senses to find an opponent’s weakness before turning on the brawn.  In a study of sidewalk cracks, a number of cases were documented in which roots had grown to a sidewalk and had followed the edge to a failed joint before growing beneath it.  Soil under cracked sidewalk blocks has a higher oxygen concentration than soil under intact blocks, which may contribute to root growth under existing cracks.

As it grows, the very tip of a root, called the root cap, protects the root because the outermost cells, known as border cells, are continually sloughing off and being replaced.  Removal of border cells quickly induces cell division in the root tip to replace the lost protective layer.

A mucous-like substance lubricates the cap surface interior to the border cells and decreases frictional resistance to soil penetration.  Friction occurs between the border cells and soil, but the lubricated root within glides forward as the border cells are released from the root cap.

Expansion of cells in an elongation zone pushes the root tip forward.  By restricting the diameter of water vessels and reducing cell layers, roots can creep into pores or slits that are narrower than other roots.  On the other hand, if a root is mechanically impeded, cell growth slows.  Cells thicken and increase the diameter of the root, and reinforcing fibers are laid down longitudinally in the cell walls.  These changes help the root apply more force and resist buckling.”  Sherry Seethaler is a UCSD science writer and educator and can be reached at sseethaler@ucsd.edu.

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