A tree’s roots, though hidden beneath the soil, form a complex and dynamic system that is fundamental to the tree’s existence. This underground network serves as the unseen foundation, actively working to procure resources and provide stability, enabling the tree to grow, thrive, and endure various environmental challenges. Without the continuous efforts of its root system, a tree cannot access necessary elements for life or maintain physical anchoring.
Water and Essential Nutrients
One of the primary functions of tree roots is the absorption of water from the soil. This process largely occurs through osmosis, where water moves from an area of higher water concentration in the soil to an area of lower water concentration within the root cells. Root hairs significantly increase the surface area for absorption, maximizing moisture intake. (1, 16) Once absorbed, water, along with dissolved mineral nutrients, travels upward through the tree’s vascular system, driven by a process known as transpiration pull. (5, 20)
Roots also absorb essential mineral nutrients, such as nitrogen, phosphorus, and potassium, present as ions in the soil solution. This uptake often occurs against a concentration gradient, requiring metabolic energy from the tree. (28) Proteins embedded in the membranes of root cells facilitate the transport of these ions into the root. (28) These absorbed minerals are crucial for metabolic processes, including photosynthesis and growth. (1)
Many tree roots form a beneficial relationship with mycorrhizal fungi. These fungi create vast networks of threads, extending the reach of the root system into the soil. (14, 24) This symbiotic association allows the tree to access water and nutrients, particularly phosphorus and nitrogen, that would otherwise be unavailable. (8, 21) In return, the tree supplies the fungi with carbohydrates from photosynthesis. (14)
Physical Stability and Support
Beyond resource acquisition, tree roots provide physical stability and support to withstand external forces. The extensive underground network anchors the tree, preventing it from toppling due to winds, storms, or gravity. (3, 7) Different types of roots contribute to this structural integrity.
Taproots, when present, grow vertically downward, offering deep anchorage and access to deeper water. (3, 4) Lateral roots spread horizontally through the upper layers of the soil, providing broad stability and absorbing nutrients from topsoil. (2, 4) Fibrous roots are fine and extensively branched, enhancing the grip on the soil and increasing foundational support. (3, 6) This comprehensive root architecture ensures the tree remains upright and resilient. (7)
Energy Storage and Specialized Roles
Tree roots serve as storage organs, accumulating carbohydrates from photosynthesis. These stored sugars and starches (non-structural carbohydrates) are crucial energy reserves. (15, 25) They are mobilized when photosynthesis is limited, such as winter dormancy, or to fuel new growth. (3, 29) These reserves also support recovery from environmental stresses or injuries. (3)
Roots play a role in the synthesis of certain plant hormones. Auxins, for instance, are plant hormones produced in growing parts, including the roots, and influence root development and plant growth. (31, 32) Roots also contribute to soil health and interact with microbial communities. They release organic compounds (exudates) that influence the composition and activity of bacteria and fungi in soil. (13, 17) This interaction enhances nutrient cycling and contributes to a healthy soil ecosystem, benefiting the tree and the environment. (10, 12)