Soil protozoa: from bacteria to plant nutrition
Protozoa consume bacteria and help release nutrients. They connect microbial biomass with plant nutrition and larger organisms within the soil food web.
Different ways of moving
In the Soil Biology Primer, Elaine Ingham introduces flagellates, amoebae and ciliates. Flagellates use flagella, amoebae form pseudopodia, and ciliates use small cilia. These single-celled organisms are larger than the bacteria forming a major part of their food.
How they release nitrogen
Bacteria contain more nitrogen relative to carbon than their protozoan consumers require. Digestion releases some surplus nitrogen as ammonium, which roots can absorb or other microorganisms can use. Ingham describes this as an important nutrient mineralisation process.
Cooperation begins near roots
The Soil Food Web School explains how exudates feed bacteria and fungi. Consumers of this microbial biomass then help release nutrients. Monitoring therefore includes both decomposers and their consumers: web function depends on their relationships.
Food and thin water films
Protozoa move in thin films of water between particles and aggregates. Moisture, aeration and structure affect where they can be active. Caring for biology includes maintaining resources and space for movement.
Food for other organisms
In 2012, Crotty and colleagues followed carbon and nitrogen from labelled protozoa in grassland and woodland soil samples. Nematodes, springtails, earthworms and insect larvae acquired protozoan-derived elements through consumption or use of biomass after death. This shows connections to higher levels of the web.
What we observe
Movement and form help distinguish groups under the microscope. We record them alongside bacteria and other sample organisms. Ingham also describes their role in regulating bacterial populations. Observations become more useful when connected with food resources and soil conditions.
Our field work
We monitor protozoa in soil, compost and liquid derivatives. Following our School training, we prepare protozoa infusions from specially managed compost to inoculate soil where their populations are reduced.