Most people may be aware that plants require 17 macro- and micronutrients to facilitate and complete their physiological processes. How do these nutrients get into the plant to support numerous plant functions? The conventional belief in agronomy has long been that plant roots get most of their nutrition solely by intercepting ions in soil solution. Recent research in soil science is challenging this notion and highlighting the role of soil microbes in nutrient cycling. Did you know that growing root tips have the capacity to absorb entire microbial cells, transforming them into beneficial organisms that provide nutrients to the plant?
Dr. James White and his Rutgers team have unraveled how plants leverage soil microbes to acquire nutrients. They have termed this process the “rhizophagy cycle” (rhizo = root and phagy = eating), wherein bacteria and fungi transition between a free-living phase in the soil and a plant-dependent phase within cells of plant roots. Microbes obtain minerals in the soil, and nutrients are extracted from these microbes in the cells of plant roots.
Lead author James F. White Jr., a professor in the Department of Plant Biology at Rutgers University, remarked, “The discovery that plants actively cultivate and extract nutrients from symbiotic microbes is groundbreaking.”
The “rhizophagy cycle” seems to occur in all land plants and could be a significant method by which plants acquire certain nutrients.
The rhizophagy cycle operates as follows: plants essentially cultivate microbes around their root tips by secreting organic acids, sugars, proteins and vitamins. These microbes then enter root cells at the tips, where cells are dividing and lack hardened walls. The microbes lose their cell walls, become trapped in plant cells and are exposed to highly reactive oxygen (superoxide). This reactive oxygen breaks down some of the microbes’ cells, effectively extracting nutrients from them. Surviving microbes then get spit out of the roots and stimulate the formation of root hairs on roots. As the root hairs elongate, bacteria exit the tips of the hairs, at which point the microbes then reform their cell walls as they reenter the soil environment. The cycle repeats over and over, according to White, who has been studying this sustainable nutrient cycle for many years.
“People have speculated that plants can get nutrients from microbes, but mechanisms for the transfer of nutrients from microbes to plants have been elusive — until now,” he said. “Understanding how this process works may allow us to grow plants without fertilizers or with minimal fertilizers and without herbicides. We can manipulate the system to increase the growth of desirable plants and decrease the growth of undesirable plants, potentially using the same microbes.”
Microbes participate in the rhizophagy symbiosis because they benefit from the nutrients provided by the host plants. This is a form of mutualism involving an exchange of nutrients between the plant and microbial participants.
The rhizophagy process is truly remarkable and challenges conventional thinking about applying fertilizers to our soil. This cycle highlights the crucial role microbes play in plant nutrient cycling. The future of agronomy and plant nutrition will likely revolve around understanding the science needed to supply the majority of a crop’s nutritional requirements through microbiology, rather than relying on simple soluble nutrients from synthetic products.
This Rutgers-led study could and should lead to enhanced crop growth, and lower fertilizer and herbicide use. This research underscores the significance of managing soil biology to optimize plant health, and should affect every grower’s soil management practices to tap into these microbial functions.
I leave it to you to decide whether this bacterial root regurgitation and nutrient acquisition process is an act of carnivorous behavior of plants. Regardless of your decision, the rhizophagy cycle must be considered not only fascinating but crucial for the future of sustainable agriculture. I will leave you with a simple mantra and applicable rule for all producers and gardeners to follow: Grow plants to feed the microbiology that literally feed your plants.