Two mutualistic interactions with soil microbes are critical to the success of terrestrial plants. Fungi and plants form mycorrhizae, which greatly increase the soil volume that roots can scavenge for nutrients. Bacteria in soils and root nodules fix atmospheric nitrogen into forms that plants and ultimately animals can use.
learning outcomes
You should be able to:
Describe the chemical signals exchanged between soil organisms and plant root cells.
Justify the need for nitrogen-
Describe crop rotation and explain how it relates to plant nutrition.
What is exchanged between plants and fungi in mycorrhizae? Between leguminous plants and bacteria in nodules?
In both cases, the plants supply the other organism with photosynthate (e.g., sugars). Mycorrhizae supply phosphorus; bacteria in nodules supply fixed nitrogen.
Earth’s biosphere as we know it depends on the existence of a few species of nitrogen-
Numerous species fix nitrogen. Loss of one species might allow populations of other species to expand and take on additional nitrogen fixation. Loss of all nitrogen-
A common cropping method is crop rotation, with corn or soybeans being rotated on a given plot of land. Explain this in terms of plant nutrition, especially available nitrogen in the soil.
The corn crop depletes the soil of nitrate. The soybeans do not require nitrate, as they have nitrogen-
Let’s turn now to some special mechanisms for obtaining nutrients that have evolved in plant species with unusual lifestyles.