Maximum Yield Australia/New Zealand March/April 2020

M icroorganisms living in the rhizosphere have a symbiotic relationship with the plants who host them. Bacteria, fungi, nematodes, protozoa, and arthropods are all beneficial microbes connected in the soil food web and working together to feed the plants in our garden. As gardeners, it helps us to learn about these beneficial microbes and how to support them, so they thrive in the soil and work to give us a healthy garden. BACTERIA One teaspoon of healthy soil contains between 100 million and one billion bacteria. These tiny, one-celled organisms are a miniscule 0.1 millimetres wide and only slightly longer in length. They are the first microbes to digest new organic matter in the soil. They recycle nutrients, suppress diseases, and improve the soil’s ability to hold water. There are four kinds of bacteria: decomposers, mutualists, lithotrophs, and pathogens. Decomposers feed on carbons, such as root exudates and plant litter. After digesting them, their waste becomes food for other soil organisms in the food web. This way, nutrients such as nitrogen are kept in the root zone instead of leaching out into the groundwater. Mutualists have symbiotic relationships with plants. For example, nitrogen-fixing bacteria make their home in the root zone of legumes and certain trees. They convert nitrogen from the air into a plant-available form. This nitrogen is then returned to the soil when the plant drops its leaves. Instead of consuming carbon compounds, lithotrophs consume nitrogen, sulfur, iron, and hydrogen. They play a role in the nitrogen recycling process and can be helpful at degrading pollutants. While bacterial pathogens can damage plants, they can be kept in check with a healthy and diverse microbial community in the rhizosphere. Other microorganisms will compete with the pathogens and keep their populations and check. FUNGI Fungi are another key player in the soil food web. These microscopic cells grow strands called hyphae that weave throughout the soil and bloom above the soil as mushrooms. They can be grouped as decomposers, mutualists, and pathogens. 40 Maximum Yield Decomposers play an important part in nutrient cycling by breaking down hard-to-digest materials, such as cellulose and lignin, and retaining the nutrients in the soil. They also help create humus, which is resistant to degradation and holds water well. Mutualists have a symbiotic relationship with plants. They colonise the root zone and send out their hyphae to create a vast underground network. The hyphae resemble roots and can travel miles underground. Plants can communicate with one another through this network and warn one another of potential threats. These mycorrhizal fungi will bring soil nutrients and water back to its host plant. Pathogenic fungi, such as Verticillium and Pythium, can reduce a harvest or kill plants completely when they colonise their root zone. However, some pathogenic fungi help to control pests and disease. For example, certain strains will set traps for harmful nematodes. Some strains create sticky traps, while others make circular rings with their hyphae to constrict and kill their prey. PROTOZOA Protozoa are several times larger than bacteria and can be classified into three groups: ciliates, amoeba, and flagellates. Ciliates consume bacteria, amoebas, and flagellates. They can eat up to 10,000 bacteria per day, and then release nitrogen in a form plants and other soil organisms will dine on. “ Fungi are another key player in the SOIL FOOD WEB. These microscopic cells grow strands called hyphae that weave throughout the soil and bloom above the soil as mushrooms.”

Maximum Yield Australia/New Zealand March/April 2020 | Page 42