Biogeochemistry of phosphorus, iron, and trace elements in soils as influenced by soil-plant-microbial interactions

The rhizosphere, a thin layer of soil adjacent to roots of living plants, is a chemically complex and microbiologically dynamic segment of the soil. At any given time, it accounts for a small fraction of the bulk soil in the root zone. All the surface soils, at one time or another, may be under the influence of roots. The rhizosphere receives exudates from roots, supports a dense and diverse population of microorganisms, and its chemistry is affected by the organic substances exuded by plant roots and by metabolites produced from microbial degradation of the organic substrates. The extraction of nutrients such as potassium ions by plants often initiates the weathering of primary minerals to secondary minerals. The biogeochemical activities in the rhizosphere have profound influence on evolution of soils. They induce dissolution of not readily soluble plant nutrients and potentially toxic elements and accelerate the weathering of clay minerals affecting the soil ability to accommodate plant nutrients and to attenuate toxic elements.