Alfalfa can have long roots and is one of 22 plant species found to develop adventitious roots in clusters along older roots. Here, a technician holds a greenhouse-grown alfalfa plant with roots 14 feet long. Click the image for more information about it.

Plant Roots, Too, Know How to "Seize the Moment"

A recent discovery by Agricultural Research Service plant physiologist Richard Zobel may lead to a "rewriting of the book" on plant roots. Zobel and a colleague have found that many plant roots commonly regrow from the same spot on a root, and that they can do this on roots deep below the soil surface.

Zobel, with the ARS Appalachian Farming Systems Research Center in Beaver, W.Va., and Dominick J. Paolillo, Jr., at Cornell University in Ithaca, N.Y., found evidence of roots growing this way on 22 species of plants from 12 different plant families in nine orders of plants. These plants included alfalfa, carrots, chicory, clover, crown vetch, dandelion, horse chestnut, lamb's-quarters, parsnip, poke weed, rock maple, thistle and tree of heaven.

Zobel and Paolillo made these discoveries while searching for plants with so-called opportunistic, or adventitious, rooting. They found adventitious roots growing in clusters along older roots. Adventitious roots grow from a different cell layer than the regular, lateral roots, so a plant that has used up the tissue available to grow regular roots can still grow adventitious roots.

These roots are called "opportunistic" because they can develop in a matter of hours, to take advantage of sudden environmental changes such as a rare rain in a desert.

The discovery that adventitious roots growing this way are an everyday occurrence suggests they may play an important and unexpected role in routinely helping plants reach water and nutrients. These roots can sprout on larger roots whose lateral roots have long since died back, enabling the plant to access water and nutrients that have recently become available in those sections of the soil that would otherwise be out of reach.

This information could also help scientists introduce adventitious roots to a crop like cotton that apparently is one of the few plants that doesn't have them, as a more efficient way for the crop to grow new roots when rain comes after a dry spell.

ARS is the U.S. Department of Agriculture's chief scientific research agency.