Submitted to: Soil Biology
Publication Type: Book / Chapter
Publication Acceptance Date: January 15, 2010
Publication Date: August 6, 2010
Citation: Dao, T.H. 2010. Extracellular enzymes in sensing environmental nutrients and ecosystem changes: Ligand mediation in organic phosphorus cycling. In: Skukla, G.C., Varma, A., editors. Soil Enzymes. Berlin, Germany: Springer. p. 75-102. Interpretive Summary: Phosphorus (P) is a nonmetallic element that is essential to living organisms. Plant available P is growth limiting and organic P contribute to plant mineral nutrition only after breakdown and release of inorganic phosphate, which is of particular importance in phosphate-deficient natural or agricultural production systems. Most of the organic P breakdown occurs in the soil near roots of plants where hydrolyzing-enzymes are released by plant roots and environmental microorganisms, allowing these organisms access to outlying P substrates that otherwise are not accessible. However, concurrent competing reactions regulate the availability of these P-containing substrates and the released phosphate for plant uptake or dispersal in the environment. Thus, to gain an accurate description of the transformations and cycling of organic P in soils and the environment, it is important to understand the relationship between plant and their roots, and microorganisms that populate land and water environments, and the processes that are involved in the cycling of P-compounds in those environments. As plant and microorganisms have evolved multiple strategies to obtain needed P, the interweaving of physical and biochemical processes in the formation of diverse chemical forms and the availability of organic P forms are often observed. A combination of ligand exchange and decomposition of organic P substances in an analytical tool appears to be a natural blend for determining organic nutrient turnover or for detecting changes in nutrient status in a particular agricultural setting; ligands play a critical role in the solubilization and breakdown of water-insoluble organic P substrates and thus, in the supply of inorganic phosphate to the soil solution to meet nutritional needs of crop plants and microorganisms.
Technical Abstract: Inorganic and organic phosphates react strongly with soil constituents, resulting in relatively low concentrations of soluble P in the soil solution. Multiple competing reactions are operating to regulate the solution-phase concentration of P-containing organic substrates and the released phosphate for assimilation by microbes, plants, or dispersal in the environment. In intensive agrosystems, external inputs of commercial fertilizers are often required to attain sufficiency levels of plant-available P. In this chapter, we focus on the ligand exchange process involved in the solubilization of organic P, a forerunner process crucial to the function of extracellular phosphohydrolases in accessing the recalcitrant soil organic P pool. Plants and microorganisms have evolved and developed multiple strategies to obtain needed P. In these strategies, frequent interweaving of biophysical and biochemical processes are observed in the mineralization of organic P forms. A fundamental reassessment of the biogeochemistry of P in the soil-water systems is necessary to improve our understanding of the physical chemistry of charged surfaces and the role of organic ligands in the turnover of stabilized organic P. Practical solutions to constraints to phosphohydrolases’ activity are needed to attain improved use efficiency of this non-renewable resource.