Enzymes of importance to rhizosphere processes

All processes and functions taking place in the rhizosphere are dominated by the activities of plant roots, rhizosphere microorganisms and root-microorganism interactions, and enzymes are recognized as main actors of all activities occurring in rhizosphere environments. Rhizosphere enzymes have, in general, a higher activity than those operating in bulk soil, as the rhizosphere soil is richer in organic C substrates. Enzymes, produced and released by both roots and microorganisms concur to altering the availability of nutrients in the rhizosphere, being implied in the hydrolysis of C-substrates and organic forms of nutrients such as N, P and S. The production and activity of rhizosphere enzymes is controlled by several factors, in turn depending on soil-plant-microorganism interactions. In general, higher activity of rhizosphere enzymes can be interpreted as a greater functional diversity of the microbial community. An interesting aspect is their involvement in the possible removal of both inorganic and organic pollutants from the terrestrial food chain. The lack of satisfying methodologies for measuring the location and activity of rhizosphere enzymes has often hampered a clear knowledge of their properties and functions. Sophisticated technologies, now available, will be helpful to reveal the origins, locations and activities of enzymes in rhizosphere. The main scope of the present paper is to cover briefly general and specific concepts about rhizosphere enzymes and their role in soil processes. Examples chosen among those published recently, supporting and confirming properties, features, and functions of rhizosphere enzymes will be illustrated.