The roots of a plant in the legume family with nodules
(the roundish bumps) where the Rhizobia bacteria live
When I think of bacteria, I think of sick people. Anthrax, leprosy, and bubonic plague as well as more minor infections all involve bacteria. And to think about a fungus makes me think about mold growing on a loaf of bread that has gotten old. To think that these microorganisms might form relationships with plants makes me concerned for the health of the plant! However, while there are plant diseases caused by these microscopic organisms, other bacteria and fungi actually help out plants.
Bacteria are the classic example of the unlikely relationships between microbe and plant. It all starts when a legume plant sends out a message looking for available Rhizobia bacteria of a certain kind. The Rhizobia respond to the call and move into the residence that the plant builds; this residence is called a nodule and looks like a small bump on the plant’s root. The plant then starts feeding the bacteria. In turn, the bacteria use their ability to take nitrogen from the air, and it gives that nitrogen to the plant. While the air is nearly 80% nitrogen, plants cannot use the nitrogen directly from the air so the service that the bacteria provide is quite valuable to the plant. In the end, both the plant and bacteria are happy and getting something from the other that they cannot produce by themselves.
Certain fungi, referred to as mycorrhizae, have a similar relationship with plants. They invade the plant’s roots and obtain food. Producing food is what a plant does well as plants are one of the few organisms that produce their own food; most organisms eat other animals or plants as their source of food. The fungus, on the other hand has a different specialty that is useful to the plant. It has an ability to explore more soil than the plant’s roots in search of water and nutrients; the fungus’ mycelium are both more abundant and smaller than plant roots so they can explore more soil. It then brings this extra water and nutrients to the plant. Mycorrhizal fungi also have the ability to alter the chemistry of the soil to extract certain nutrients that the plant could not get on its own. These fungi seem to be especially important in the acquisition of phosphorus. Many plants, but not all, have a relationship with mycorrhizae, and wherever these relationships exist, they benefit both plant and fungus.
Since not all plants form a relationship with nitrogen-fixing bacteria or water and nutrient-acquiring fungi, it is important to have a diversity of plants. After the plant that hosts the microorganism uses the nutrients, they can be recycled in the soil and used by other plants that do not have the ability to form these relationships with bacteria and fungi. For folks aiming to produce forage for livestock, these relationships are the equivalent of free fertilizer. Having these plants means the production of more forage for livestock. For wildlife enthusiasts, these microorganism-plant relationships produce food (e.g. foliage and seeds) that are more nutritious (e.g. higher in protein and minerals). Landscapers, who are always concerned about blooms, should see more blooms where more nutrients are available; it is the equivalent of a bloom-booster fertilizer. Lastly, those folks interested in restoring glades, prairies, and savannas should appreciate these relationships, if for no other reason, just because they are a part of our native grasslands. A diversity of plants yields a diversity of relationships with microorganisms which, in the end, is beneficial to us humans.