Rhizosphere (ecology)

The rhizosphere is the narrow region of soil that is directly influenced by root secretions and associated soil microorganisms. The rhizosphere contains many Bacteria and microorganisms that feed on sloughed-off plant cells, termed rhizodeposition, and the proteins and sugars released by roots. This symbiosis leads to more complex interactions, influencing plant growth and competition for resources. Much of the nutrient cycling and disease suppression needed by plants occurs immediately adjacent to roots due to root exudants and communities of microorganisms. The rhizosphere also provides space to produce allelochemicals to control neighbors and relatives. The plant-soil feedback loop and other physcial factors are important selective pressures for the communities and growth in the rhizosphere.

Exudates, such as organic acids, change the chemical structure of the rhizosphere in comparison with the bulk soil. Concentrations of organic acids and saccharides affect the ability of the plant to uptake Phosphorous, Nitrogen,Potassium and water through the root cap, and the total availability of Fe to the plant and to its neighbors. The ability of the plant to affect the availability of Fe and other minerals for its neighbors by providing specific transport proteins affects the composition of the community and fitness.

Exudates come in the form of chemicals released into the rhizosphere by cells in the roots and cell waste referred to as "rhizodeposition." This rhizodeposition comes in various forms of organic carbon and nitrogen that provide for the communities around plant roots and dramatically affect the chemistry surrounding the roots. Exopolysaccharides, such as PGA, affect the ability of roots to uptake water by maintaining the stability of the rhizosphere and controlling the flow of water. In potato cultivars, phenols and lignins comprise the greatest number of ion influencing compounds produced as plant exudates regardless of location; however, the intensity of different compounds was found to be influenced by soils and environmental conditions, resulting in variation amongst N compounds, lignins, phenols, carbohydrates, and amines.

Chemicals connected to allelopathy: flavinols carbohydrates and application by root hairsphenols Positive Allelopathic pathways and definitions of interactions between plant-plant and plant-microbe, positive plant-microbe in the form of systematic resistance

Although it goes beyond the rhizosphere area, it is to note that some plants secrete allelochemicals from their roots which inhibit the growth of other organisms. For example, garlic mustard produces a chemical which is believed to prevent mutualisms forming between the surrounding trees and mycorrhiza in mesic North American temperate forests where it is an Invasive species.

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