Effects of heavy metal stress on the metabolic quotient of the soil microflora

A variety of quantitative measurements such as viable counts, microbial biomass (Cmic), respiration, enzyme activities or ATP contents may be used to study the effects of heavy metals on the soil microflora (Babich and Stotzky, 1985; Brookes et al., 1986). Studies on biochemical abilities of certain isolates, such as heavy metal resistance, have also been made (e.g. Schmidt and Schlegel, 1989). Few papers address the physiological status of the microbial community. Among them are studies on the metabolic quotient (qCO2), which is respiratory CO2 release per unit biomass. A change of qCO2 may indicate (i) changes in substrates that an unchanged community uses, (ii) a change of community composition, (iii) a change in both (i) and (ii), (iv) no changes of substrates or community, but a change in the physiological status of the community due to altered maintenance requirements. The results of the studies on qCO2-response upon heavy metal contamination, however, are contradictory, since some authors reported an increase (Brookes and McGrath, 1984; Flieكbach et al., 1994; Ortiz et al., 1993) and some a decrease of the qCO2 (Bههth et al., 1991).