One of the foundations of life in the garden is the interaction between various root systems and soil. In addition to acting as a support and anchor for the growing plant, these systems transport water and nutrients from the soil upward through the stalks, leaves, and stems.
The origination point for the root is the seedling’s bottom portion. As the seed germinates and sprouts upward, the taproot grows straight down. This primary root may extend several inches in the soil before a developing shoot emerges above ground. Over time, with plants such as onions and corn, the primary root is replaced by a mass of small, stringy roots. As with spinach and carrots, the taproot remains the dominant root across the plant’s lifespan.
Plants like tomatoes develop side or lateral roots that branch out from the primary root. Meanwhile, strawberries sprout adventitious roots from runners, stems, and leaves, supporting new fruits and berries as they mature.
Plants require soil with an oxygen component, which helps avoid the buildup of gaseous carbon compounds that choke and kill roots. Proper oxygenation is ensured through the use of less dense, porous soil, including that that incorporates lava, pumice, and bark. Ideally, soil should have 50 percent air space, which maximizes oxygen diffusion.
The root-to-soil relationship is not static, with root hairs and tips, the most tender and newest parts of the root, continually probing deeper into the soil for nutrients and water. The hairs and tips of the plant root absorb such nutrients and pump them via xylem, or hollow cells, to the stems and leaves.
This is enabled through photosynthesis, a process related to light exposure, with dissolved glucose sugar produced in the shoots and leaves and sent back down to the roots via phloem, another system of hollow cells. As these sugars combine with nutrients such as nitrogen, they provide the energy roots require for proper function and growth.
At the level of microorganisms, the “rhizosphere” is a term used to describe the area around the plant root, characterized by specific chemical, physical, and biological properties conditioned by the roots. One aspect of this is the pressure exerted by growing root tips as they push their way through the soil. Lubricating their path and protecting them is viscous, polysaccharide-rich mucilage. This secretion enables nutrient acquisition and helps bind together soil particles, forming aggregates that boost water infiltration, aeration properties, and overall soil quality.
Roots also benefit from mycorrhizae or a symbiotic relationship with soil fungi. The fungus works with the plant root to absorb dissolved minerals such as phosphorus and pass them on to the plant root via the mycelium. The plant root then passes organic compounds such as sugars and photosynthetically fixed carbon to the fungus.
There are various types and structures of mycorrhizal associations, with ectomycorrhiza and endomycorrhiza defining the two basic ways fungi interface with the plant roots. Most within the endomycorrhiza category are arbuscular mycorrhiza (AM) fungal associations, with plants such as orchids and cranberries having specialized mycorrhizal associations.
Specific types of soil bacteria also maintain symbiotic relations with legume family members, including clover and beans. Performing nitrogen fixing, they infect roots and cause a round swelling in the root known as a nodule. Consuming a certain amount of sugar produced by the root, the bacteria release nitrogen from the air in the soil. This is fixated or converted into the types of nitrogen compounds that plant roots absorb and require for energy.
