Home Cellular health Roots Eat Bacteria – Ohio Ag Net

Roots Eat Bacteria – Ohio Ag Net

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By James Hoorman Hoorman Soil Health Services

(Source: Jeff Lowenfels, Teaming Up With Bacteria, 2022)

Do plant roots really eat bacteria? The answer is yes (sort of!). Over the past 5-10 years, our understanding of how plants acquire nutrients has changed dramatically. With new, more powerful microscopes; An Australian scientist and Dr. James White of Rutgers University have discovered that plant roots absorb endophyte bacteria (translation: “in the plant”) and acquire nutrients from these microbes. One study estimates that 47% of atmospheric nitrogen (N) and possibly as much as 70% of plant nitrogen could be acquired from bacteria absorbed and living between plant cells and inside cells plants. This newly discovered process is called rhizophagy.

We shouldn’t be too surprised. Farmers inoculate legumes (soybeans, peas) with Rhizobium bacteria that reside in plant nodules and fix N. Arbuscular mycorrhizal fungi (AMF) also penetrate roots and live between plant cells. AMFs are like root expanders, bringing water and nutrients back from the soil in exchange for plant sugar. Endophyte bacteria do the same thing and all three (Rhizobium, AMF, bacteria) use similar processes to enter the plant. Important note: This is a symbiotic relationship (mutually beneficial for both parties) and the plant is the one that initiates and controls this process.

There are three plant zones for acquiring nutrients. First, loose soil away from plant roots contains many nutrients. The AMF can extend 6 to 18 inches from a root to access water and nutrients that a root cannot reach. Second, the rhizosphere all around plant roots sends out root exudates to communicate or signal to certain microbes what plants need nutritionally. Plants feed microbes and microbes make nutritious plants available. The third zone is now made up of endophyte microbes that live in the plant by supplying nutrients through rhizophagy.

The rhizophagy cycle is complex and very tightly controlled by plant roots to avoid root cell damage. Bacteria cluster and live in dense biofilms around the root cap (root tip). Biofilms are packed with nutrients (exudates from plant roots) and provide protection from predators. These bacteria make the nutrients available to the plant, but the plant wants more because it wants to grow (think teenagers and how much food they need to grow fast). The plant signals certain bacteria to enter the membranes of thin-walled root cells (meristem cells) near the root cap. Bacteria use arginine (a plant amino acid root exudate) to make ethylene to enter the roots. Once inside the root, these bacteria shed their cell wall (think tumbling through a washing machine) but they are still alive. Some remain between the cell walls, others enter the plant cell themselves or move to other parts of the plant (stems, leaves, flowers, seeds).

The cell wall stripped of endophytic bacteria provides a banquet for the plant. Carbohydrates (sugars), amino acids, plant growth hormones, and macro and micronutrients are all released into the hungry plant for faster growth and higher yields. The wallless bacteria thrive in the protected plant (lots of food, no predators, little stress) and multiply extremely quickly (every 20 minutes). As the microbial population grows, it becomes crowded, so they begin to grow outward forming a new root hair. Root hairs can only form from endophyte bacteria! These bacteria invade the root hairs in such numbers that they are expelled in waves through the soil. Once in the soil, these bacteria fatten up with nutrients, grow a new cell wall, and begin looking for the next trick in the plant. The whole process takes about 2 days.

A few bacteria do not survive this mad dash (perhaps up to 10%). Inside a bacterial cell, the cytoplasm is full of nutrients and intact phytohormones that greatly stimulate plant growth, which in the long run is good for healthy plants and healthy microbial populations in the long run. Since bacteria often divide and produce by division, they really don’t have an individual lifespan unless they die or are consumed by another organism.

There is no difference between plant nutrients derived from rhizophagy and those derived directly from the soil. The big difference, root feeding provides the plant with easy to get nutrients when it is really hungry and wants to grow and produce seeds. Intact Plant Growth Hormones stimulate rapid growth and increase crop yields. Moreover, endophytic bacteria produce nitric oxide to protect themselves inside the plant. This nitric oxide is converted into nitrates which the plant can use directly and be converted into plant N to make amino acids, proteins and enzymes. This new information could help farmers and gardeners grow nutrient-dense, high-yielding crops with far less commercial fertilizer in the near future.