Influence of cadmium on the metabolic quotient, L-: D-glutamic acid respiration ratio and enzyme activity : microbial biomass ratio under laboratory conditions
L. Landi et al., Influence of cadmium on the metabolic quotient, L-: D-glutamic acid respiration ratio and enzyme activity : microbial biomass ratio under laboratory conditions, BIOL FERT S, 32(1), 2000, pp. 8-16
This study was carried out to investigate the effect of very high cadmium c
oncentrations (50 and 500 mug Cd g(-1) soil) on some biochemical and microb
iological measurements under laboratory conditions involving daily soil sam
plings. The data for both DTPA and water-soluble Cd showed two distinctive
patterns during soil incubation; from 0 to 4 days, values were about 50-500
and 1-100 mug g(-1) dry weight soil, whereas they decreased markedly after
7 days. Both daily respiration and the ATP content but not the microbial b
iomass C determined by the fumigation-extraction method were lowered by hig
h DTPA- and water-soluble Cd concentrations. Dehydrogenase and phosphatase
activities as well as both enzyme activity:microbial biomass ratios were de
creased by the high DTPA- and water-soluble Cd concentrations. In the first
2 days of incubation, the metabolic quotient (qCO(2)) was also decreased b
y the highest values of available Cd. The early (after 6 h) mineralization
of L- but not D-glutamic acid to CO2 was inhibited during the 0-4 day incub
ation period by the highest Cd concentration. Possibly the L-enantiomer was
used by a larger fraction of soil microorganisms than the D-enantiomer or,
if they were used by the same fraction of soil microorganisms, the D-enant
iomer was mineralized at a lower rate. The L-:D-glutamic acid respiration r
atio was decreased by the high available Cd content because under polluted
conditions soil microorganisms probably discriminated less between the two
stereoisomers of glutamic acid.