Krishan Chander

Decomposition of 14C glucose in two soils with different amounts of heavy metal contamination

A high metal-containing soil and a low metal-containing soil were supplied with 14C-labelled glucose at two rates, one to provide a constant glucose-to-soil ratio and the other a constant glucose-to-biomass ratio. The aim was to assess the effects of these different ratios on the microbial substrate utilisation efficiency. Glucose was added with or without N to investigate the extraction efficiency of the fumigation-extraction method shortly after substrate addition. The addition of glucose without N resulted in a proportionally larger increase in microbial biomass C than in microbial ninhydrin-reactive N (ENIN) within the first few days after substrate addition, due to N deficiency. The biomass C-to-ENIN ratio remained constant in all soil treatments after glucose addition in combination with N, indicating that the extraction efficiency of the fumigation-extraction method is not affected by the addition of glucose. Lower percentages of glucose added were incorporated into the microbial biomass with an increasing ratio of glucose-to-biomass. The ratio of respired to biomass incorporated 14C increased in all high metal-containing soil treatments markedly above that of the low metal-containing soil from day two of the incubation, markedly overriding the effects on the glucose C-to-biomass C ratio. Our results clearly demonstrated that more substrate was diverted by microorganisms into catabolic at the expense of anabolic processes in a high metal-containing soil.

Comparison of methods for measuring heavy metals and total phosphorus in soils contaminated by different sources

The relationships between the concentrations of zinc (Zn), lead (Pb), copper (Cu), nickel (Ni) and chromium (Cr) as measured by X-ray fluorescence analysis (XRF), aqua regia, and HNO3 pressure digestion were studied in soil samples covering a wide range of heavy metal concentrations. The soils were contaminated by sewage sludge, exhaust depositions, river sediments of mining residues, and dump material. The question was addressed whether the source of heavy metals or other soil properties affect the relationship between these three methods. The aqua regia-digestible fraction of the five heavy metals reached on average 64% of the XRF-detectable content. The pressure accelerated HNO3-digestible fraction of the five heavy metals was on average 71% of the XRF-detectable content; the respective phosphorus (P) fraction reached a median of 75%. This suggests that HNO3 pressure digestion can also be used for characterizing the total P content of soils. Aqua regia extraction and HNO3 pressure digestion gave similar values for Zn, Pb, and Cu, which dominate the heavy metal load of most contamination sources. Significantly higher Cr values were obtained by HNO3 pressure digestion than by aqua regia extraction. Additionally, the Cr contents were affected by the source, e.g. sewage sludge had relatively high contents of aqua regia and HNO3 pressure extractable contents in comparison to the XRF values. The element-specific relationships between the three methods were all highly significant. However, the respective multiple linear regression models were in most cases affected by soil organic carbon (C), in some cases by clay or soil pH.

Long‐term effects on soil microbial properties of heavy metals from industrial exhaust deposition

Soil samples were taken at 0-10 cm and 10-20 cm depth from 7 clay-marsh sites used as grassland close to Nordenham in the north of Lower Saxony, Germany. The sites had been contaminated by deposition of heavy metals from industrial exhausts, the level of contamination varying according to their distances from a lead factory. The soils were analyzed to assess the depth-specific effects of NH 4 NO 3 extractable and total amounts of Zn, Pb, and Cu on basal respiration, adenylates, ergosterol, and biomass C estimated by fumigation extraction (FE) and substrate-induced respiration (SIR). Most of the chemical and biological properties studied decreased with depth, but depth-specific differences in the relationships between these properties rarely occurred. The biomass C/soil organic C ratio was at a relatively high level, but most consistently reflected pollution as a decrease with increasing heavy metal load, independently of the method used for biomass C estimation. However, the SIR estimates were on average 44 % lower than those of FE, mainly due to pH effects. The metabolic quotient SIR- q CO 2 increased with increasing NH 4 NO 3 extractable and total heavy metal contents, but also with decreasing pH, whereas the FE- q CO 2 remained unaffected by heavy metals and pH. The ATP/FE-biomass C ratio was on average 8.2 μmol g -1 and negatively affected by soil pH, but also by total Zn, NH 4 NO 3 extractable Zn and Cu. The ergosterol/FE-biomass C ratio was on average 0.29 %, i.e. at a very low level, and increased with increasing heavy metal content. This indicates a change in the community structure towards fungi.

Decomposition of 14C labelled glucose in a Pb-contaminated soil remediated with synthetic zeolite and other amendments

Abstract In an incubation experiment, we assessed the effects of a synthetic zeolite (type 4A) on biomass and community structure of soil microorganisms in a highly Pb-contaminated soil. The effects of zeolite were compared with other amendments that increase soil pH, such as CaCO3, or improve microbial properties, such as compost. In a separate experiment, the effect of the different amendments on the efficiency of microbial substrate use was determined using 14C labelled glucose. The amendments led to significant increases in pH and decreases in NH4NO3-extractable Pb. A 99% decrease in extractable Pb was only observed in the treatments containing CaCO3. The addition of the synthetic zeolite 4A gave a 69% and that of compost a 10% reduction. The addition of zeolite and CaCO3 mobilised soil organic matter as indicated by increased contents of CaCl2 extractable C and increased CO2 production rates. Microbial biomass C was increased by all amendments, but in most cases it was not significant. Maximum biomass C was measured where the combined amendment zeolite+compost+CaCO3 was added. The addition of compost, especially when combined with CaCO3, resulted in an increased ergosterol content. In contrast, the sole addition of synthetic zeolite had a significant depressive effect on the ergosterol content and, thus, on the ergosterol-to-biomass C ratio. The most striking feature of the treatments containing synthetic zeolite was the effect on glucose decomposition. Zeolite increased both incorporation of 14C into microbial biomass and mineralisation to 14CO2, so that the ∑CO2-14C-to-biomass 14C ratio remained unaffected.

Microbial biomass and activity indices after organic substrate addition to a selenium-contaminated soil

High concentrations of Se in soil might have negative effects on microorganisms. For this reason, the effect of organic substrate addition (glucose + maize straw) on Se volatilisation in relation to changes in microbial biomass and activity indices was investigated using an artificially Se-contaminated soil. Microbial biomass N was reduced on average by more than 50% after substrate addition, but adenylate energy charge (AEC) and metabolic quotient qCO2 were both increased. The Se content decreased by nearly 30% only with the addition of the organic substrate at 25°C. No significant Se loss occurred without substrate at 25°C or with substrate at 5°C. In the two treatments with substrate addition, the substrate-derived CO2 evolution was about 30% lower with Se addition than without. In contrast, Se had no effect on any of the other soil microbial indices analysed, i.e. microbial biomass C, microbial biomass N, adenosine triphosphate (ATP), AEC, ATP-to-microbial biomass C, and qCO2.

Soil microorganisms and the growth of Lupinus albus on a high metal soil in the presence of EDTA

A pot experiment was designed with the objective of determining whether the presence of ethylenediaminetetraacetic acid (EDTA) and the resulting mobilization of heavy metals have any affect on: (i) soil microorganisms, (ii) growth of L. albus, and (iii) microbial colonization of roots. There was no effect of the different treatments on the contents of soil microbial biomass C and microbial biomass N. Increasing addition of EDTA to soil led to proportionate increases in extractable C and N, being roughly equivalent to the added amount. Increasing EDTA addition to soil led also to a proportionate increase in mobile heavy metals. Plant height, total amount of shoot and root C were not affected by EDTA addition. Fungal ergosterol in the lupine roots showed a 5- to 8-fold increase in the 0.1 and 0.2% EDTA treatments in comparison with the control. In contrast, EDTA addition did not affect fungal glucosamine or bacterial muramic acid concentrations in the lupine roots. Increasing EDTA addition to soil led also to a proportionate increase in the metal concentrations in the lupine shoots. The concentrations of heavy metals in the lupine shoots and in the NH4NO3 soil extracts were all highly significantly correlated.