Enzymes of importance to rhizosphere processes

Abstract

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.

Enzymes in the rhizosphere of plants growing in the vicinity of the Polish Arctowski Antarctic Station

“…At different sites the plant cover might be influencing the structure and size of the rhizospheric microbial communities, which in turn are responsible for the different extracellular enzyme patterns present in soils (Yergeau and Kowalchuk, 2008;Zeglin et al 2009;Gianfreda 2015). Since the sample size from the and low pH (5.1) (Cuba et al, 2010).…”

“…The associations with rhizospheric microorganisms (fungi and bacteria) and the presence of several soil enzymes can play an important role in the adaptation and survival of these plant species in extreme environments like Antarctica. For instance, some hydrolases in the soil like phosphatase, b-glucosidase and urease, are key to the biogeochemical cycles of P, C and N, respectively, contributing to plant nutritional status (Nannipieri et al 2002;Ali et al 2015;Gianfreda 2015). Soil enzymes have been used as indicators of microbial activity and the health and quality of soils, mainly in extreme environments, where they show the relative availability or limitation of energy or nutrient sources (Hopkins et al 2008;Cowan et al 2014).…”

The biological activities of β-glucosidase, phosphatase and urease as soil quality indicators: a review

“…Intracellular enzymes can be found in various parts of proliferating living cells (Nannipieri et al, 1998). Living cells, however, produce and secrete extracellular enzymes which function outside the parent cells as free enzymes in a soil solution or as enzymes that are still associated with the external surface of the root epidermal or microbial cell wall (Gianfreda, 2015). These enzymes are not only available in dead cells, but may also be taken up on clays or integrated into humic substances.…”

“…Microbial species release enzymes into the environment in order to degrade complex organic molecules into absorbable simple molecules (Almeida et al, 2015). Thus, soil enzymes catalyze and increase several biochemical reactions (Gianfreda, 2015) that bring about the decay of organic residues, transformation of native soil organic matter, mineralization of nutrients for plant growth, and soil aggregation (Balezentiene, 2012).…”

Effect of wasterwater sludge application on enzyme activities in soil contaminated with crude oil

“…Enzyme activities have been demonstrated as indicators of biogeochemical cycles, the degradation of organic matter and soil remediation processes; thus, these enzymes can determine, together with other physical or chemical properties, the quality of the soil (Gianfreda 2015). Dehydrogenase oxidises soil organic matter through the transfer of protons and electrons from substrates to acceptors.…”