soil - Lublin

AERATION STATUS OF SOIL AND ENZYME ACTIVITY
Brzezińska M.
Soil is naturally exposed to the fluctuation of wet and dry cycles and to diurnal
and seasonal temperature gradients. Thus, under field conditions, soil air-water
status plays an important role in the regulation of the composition and metabolic
activity of soil microorganisms. Moreover, air-water relations in soil are strongly
effected by soil management. The kind of fertilization, the type and degree of tillage
and other agricultural practices influence many physical characteristics such as
aggregate stability, pores distribution, retention properties, and implicate alteration
of numerous chemical and biological processes (Gliński and Stępniewski 1985;
Lipiec and Stępniewski 1995; Kandeler et al., 1999; Walczak et al., 2002). Flooding
the soil creates conditions markedly different from those of a well-drained,
aerobic soil. In addition to retardation of gaseous exchange between soil and air,
waterlogging results in the changes to microbial populations and in series of physico-chemical
and biochemical transformations. Numerous permanently anaerobic
aggregates and microhabitats occur also in well-aerated soils. In the absence of molecular
oxygen, anaerobic microorganisms (facultative followed by obligatory) utilize
oxidized soil components as terminal electron acceptors in processes involved
in respiration metabolism. In the result, a stepwise reduction of soil system takes
place, soil redox potential (Eh) decreases, pH alters, and concentrations of reduced
forms increase (Gliński et al, 1996; Gliński and Stępniewski 1985; Ottow 1982).
This paper refers to the effect of the deterioration of soil aeration status on the
activities of selected soil enzymes.
SOIL AERATION AND OXIDOREDUCTASES
Oxidoreductases are involved in respiration processes of all soil microorganisms.
Dehydrogenases catalyze the transferring of hydrogen and electrons from
oxidized substrates to acceptors. Thus, dehydrogenases take part in energy accumulation
and are active in all soil microorganisms – aerobic as well as anaerobic.
Many different intracellular enzymes or enzyme systems contribute to the total soil
dehydrogenase activity. Assays for dehydrogenase activity in soil has often been
used to achieve an index of total soil microbial activity.
Soil dehydrogenase activity increases under anaerobic conditions. This tendency
has been observed in model experiments (with soils incubated at diminished
oxygen concentration or under soil flooding) as well as under natural field conditions
(Gliński et al., 1983; Okazaki et al, 1983; Pedrazzini and McKee, 1984; Tiwari
et al., 1989). The anaerobic respiration is less efficient than aerobic (with
utilization O 2 as terminal electron acceptor). Increased dehydrogenase activity under
prolonged soil hypoxia suggests that the facultative and anaerobic members of
the microbial community become more important in the total soil respiration. Soil
sampled from natural sites, characterized by extremely different oxygenation con-
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