Teeming with Microbes
An Organic Gardener’s Guide to the Food Soil Web
Article by Paul Gaylon
Inspired by the book “Teeming with Microbes”
by Jeff Lowenfels & Wayne Lewis
Rhizosphere: The region of soil surrounding plant roots where interactions between roots & soil environment occur; roots interact with microorganisms, bacteria, fungi, organic matter, nematodes, protozoa, worms, etc. Roots release carbohydrates (sugars) and protein into the soil. All roots compete for water and minerals from the soil to absorb nutrients. Bacterium and fungi utilize root exudates via ingestion. Nutrients from these interactions are absorbed and cycled back up the plant roots continuing the Soil Food Web. Plants can slow down or speed up this cycle.
The Soil Food Web provides nutrients for plants and breaks down food waste. Soil contains worms and other living organisms and produce minerals and beneficial bacterium. Certain types of bacteria and fungi exude inhibitory compounds near the roots which protect plants from pathogenic bacterium and fungi. They also produce vitamins and antibiotics which enhance overall soil health. During photosynthesis, plants combine water and carbon dioxide from the atmosphere to create carbon and sugars which it releases into the soil. Soil organisms decompose the sugars and carbon and convert them, as well as other matter present in the soil, into other nutrient forms, some of which are made available to plants. The Soil Food Web is a continous loop in which plants feed the soil and the soil feeds plants.
The Soil Food Web approach is helpful with all aspects of plant growth including water retention, aeration, mineral breakdown, decomposition, soil texture, and nutrient production. Too much bacteria in the soil lead to a larger amount of NO3 which can cover crops and grasses. The number of bacteria in soil should be less than or equal to the number of fungi. Fungi help increase growth in trees, shrubs, perennials, grasses, and virgin forests exponentially! The number of fungi and bacteria present correlates to the length of time the tree or plant has had to establish itself. (from foodsoilweb.com)
Good soil composition is composed of about 1/3 sand, 1/3 silt, and 1/4 clay. Organic matter makes up the rest of the composition. Nitrates (NO3) and chemicals harm soil. Ammonium (NH4) is more bioavailable in better soils.
Fungi usually take up more complex nutrients including those that occur from cellulose breakdown. Fungi use plant exudates to bring food back to root tips. Chemicals secreted by fungi help provide minerals and nutrients from the soil; they free up nutrients and bring back phosphorous. Phosphorus helps with energy production (Page 130). Fungi add to the decay and utilization of algae. An example is the rice plant which gets N2 from water via algae. Good results have been seen throughout Asia. Fungi have had a symbiotic relationship with soil microbes and aquatic plants (algae) for 450 million years!
Mycorrhizae fungi are a special type of fungi that have a symbiotic relationship with plant roots. Nutrients are mineralized and cycled down. 90–95% of plants produce mycorrhizae fungi which are quite beneficial. They increase root surface area and holding capacity; they also stimulate root growth, enhance nutrient and water uptake, are drought-tolerant, and help curb root shock. Mycorrhizal fungi benefit the entire plant rooting area (Page 70).
Mycorrhizal fungi obtain the carbohydrates (energy) that they need from the host plant’s exudates. They use this energy to extend out into the soil; they pump moisture and mine nutrients from areas that plant roots cannot access. Water fills porous areas in the soil and important bio-electrical connections are able to occur between roots and soil.
Bacteria have genetic material that is not enclosed by nuclei. They are simple sugars derived from plant roots and they help the soil evolve and change. Bacteria release N2 (nitrogen) from NH4 (ammonium nitrogen) to fix plant nodes. Cyanobacteria are photosynthetic microscopic organisms with a high nutrient content that are technically bacteria. They live in a diverse range of environments, from freshwater and marine environments to terrestrial ecosystems. Cyanobacteria can tolerate and live in the most extreme habitats including geothermal habitats, frozen systems, and hypersaline environments. They have existed on Earth for approximately 3,500 million years!
Hyphae are fungal strands that live and grow in soil. They attach to soil particles, deliver water and oxygen throughout the soil, and create tunnels while branching out.
Legumes enter plant roots through the root nodules. Plants provide bacteria along with oxygen, carbon, and protein as nutrients in addition to providing them with a place to live. Bacteria travel with exudates via hyphae.
Glomalins are glycoproteins that hold soil particles together. Complex interactions occur within the soil (& its PH) during the processes of decomposition and releasing of nutrients.