The rhizosphere: how roots feed soil life
An active microbial community develops around living roots. Plant-released substances feed this life, connecting photosynthesis with nutrition in soil.
Life gathers near the root
The rhizosphere is the soil zone directly influenced by roots. In the Soil Biology Primer, Elaine Ingham describes concentrated bacteria and the protozoa and nematodes feeding on them. Many feeding interactions occur beside the point where plants take up nutrients.
Exudates feed the community
Roots release soluble sugars, amino acids and other organic compounds. These exudates and cells shed from root surfaces supply microbial food, bringing photosynthetic energy into a particularly active part of the soil.
Food moves through the web
The Soil Food Web School connects exudates with bacterial and fungal growth. Microbes use organic materials and retain nutrients in biomass. Consumers release some of those nutrients in available forms. Caring for roots therefore includes caring for the community connecting them with surrounding soil.
Research around the root
In 1984, R. N. Ames, C. P. P. Reid and Elaine Ingham studied potted Bouteloua gracilis with and without a mycorrhizal fungus. They recorded bacterial populations inside and outside the rhizosphere. Mycorrhizal symbiosis was associated with different responses among the bacterial groups studied, illustrating the complexity of plant, fungal and bacterial relationships.
Space for water and air
Microbial life also helps form structure. Bacterial substances bind particles; fungal hyphae connect microaggregates. Spaces between them accommodate water, air and roots. Nutrition and structure are connected functions of the same living system.
Living roots and residues
Living roots provide readily available compounds, while residues also contain more complex materials transformed gradually. Observing these zones connects organisms with their available food.
Our field work
We plan to examine microbiology near olive roots and connect observations with compost and liquid applications, following our Soil Food Web School training.