root [ root, root ] noun: the usually underground part of a vascular plant that originates usually from the hypocotyl and lacks nodes, leaves, and buds. It functions to absorb water, nutrients, and air from the soil and expands underground to anchor and support the plant and control soil erosion
radicle [ RAD-i-kuhl ] noun: embryonic root; that part of a plant embryo that develops into the primary root
primary [ PRAHY-mer-ee, -muh-ree ] root noun: the root of a plant that develops first and originates from the radicle
Roots are the “hidden half” of plants, the underground structures that link them to the earth. Every plant seed contains an embryonic root, the radicle, which is the first part of the plant to emerge during germination. It burrows into the ground, becoming the primary root, which anchors the seedling. The roots absorb water and nutrients, which are transported through vascular bundles to the rest of the plant, allowing it to grow and thrive. Because roots are understood to be critical to survival, the word is often used as a metaphor for the base or origin of a belief, a structure, a whole discipline, study, or way of life. However, in the plant world, roots are one of the areas where research lagged for a long time and there are still great gaps in scientific knowledge.
Photo © B. Domangue CC BY-SA 4.0
For many years, when herbaria were often the centers for the collection of academic knowledge about plants, roots were particularly neglected. Partly this is understandable. Roots are underground, you have to dig them up, and when you do, the plant often dies. Roots are messy, bringing dirt and contaminants into the storage spaces, threatening to spread bacteria or fungi throughout the herbarium. They take up space, usually equal to the biomass of the above-ground or shoot portion of the plant, and in the case of trees that mass could be so large as to be prohibitive of bringing it in. Adding roots to the discussion on a typical herbarium sheet would have complicated the standard process and overrun the space for classifying and describing the plants. For centuries, only about a quarter of plants in herbaria included roots in their samples at all.
Nevertheless, over the years, there were always a few scientists who persisted in root study, sometimes watching through the sides of glass containers, other times tracking nutrient travels through the plants with dyes or, later, radioactive biomarkers. In recent decades, scientists have begun to better understand the critical role of roots and their accompanying microorganisms in the success of plants. Through these studies, botanists, foresters, and other scholars are realizing the importance of roots in the success of agriculture and food crops, forests, erosion control, and coping with climate change.
Yet because root research in situ is difficult, there is still a great deal we do not thoroughly understand about the structures, cell components, and functions of roots. Perennial plants, trees, and shrubs pose more difficulty than annuals, as their roots remain in the soil as it changes from year to year.
Researchers have learned that roots are agile adapters, often changing shape and volume and direction in accordance with the below-ground circumstances they encounter in the soil. Some are strong enough to crack sidewalks, burst pipes in search of water, and lift enormously heavy rocks. Hence, laboratory grown specimens, whether in pots or a hydroponic medium, do not necessarily equate to how roots function in the ground. The evidence of scientists who study the relationship between roots, soil, and microorganisms including mycorrhizal fungi and bacteria has also broadened our understanding that roots do not function in isolation but as part of a larger system.
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References
Bender M. March 19, 2024. These Researchers Are Digging Into the Understudied Science of Roots; After centuries of neglect, botanists are using new techniques to understand roots. Smithsonian Magazine, Science.
Michaels T, Clark M, Hoover E, Irish L, Smith A, Tepe E. 2022. Chapter 3.3 Roots. The Science of Plants. University of Minnesota Department of Horticultural Science.
Ryan P, Delhaize E, Watt M, Richardson AE. August 2016. Plant roots: understanding structure and function in an ocean of complexity. Annals of Botany. 118(4): 555–559. doi:10.1093/aob/mcw192.
Schalau, J. February 2020. Backyard Gardener: Understanding Plant Roots. University of Arizona Cooperative Extension, Yavapai County.