M. De Nobili

Bioavailability and effects of heavy metals on soil microbial biomass survival during laboratory incubation

In this work we studied the influence of Pb, Zn, and Tl on microbial biomass survival and activity during a laboratory incubation of soil. In comparison to uncontaminated soil, the microbial biomass C decreased sharply in soil contaminated with Zn and Tl, whereas the addition of Pb did not have any significant inhibitory effect on the level of microbial biomass C. Zn displayed the greatest biocidal effect, confirmed by the measurement of the death rate quotient (q D). The microbial activity, measured as CO2 evolution, increased significantly in contaminated soils, emphasizing the need of living organisms to expend more energy to survive. The greater demand for energy by microorganisms in order to cope with the toxicity of pollutants was also confirmed by measurement of the metabolic quotient (q CO2). In order to determine whether soil microorganisms affect the bioavailability of these metals through their mobilization and release, we studied the relationships between available Pb, Zn, and Tl, and microbial biomass C. The water-soluble fraction of Tl, available Tl, and Zn, and microbial biomass C were related significantly, but not Pb.

Influence of inorganic and organic fertilization on soil microbial biomass, metabolic quotient and heavy metal bioavailability

Abstract We studied the long-term effects (12 years) of municipal refuse compost addition on the total organic carbon (TOC), the amount and activity of the microbial biomass (soil microbial biomass C, BC and metabolic quotient qCO2) and heavy metal bioavaiability in soils as compared to manuring with mineral fertilizers (NPK) and farmyard manure (FYM). In addition, we studied the relationships between among the available fraction [Diethylenetriaminopentacetic acid (DTPA) extractable] of heavy metals and their total content, TOC and BC. After 12 years of repeated treatments, the TOC and BC of control and mineral fertilized plots did not differ. Soils treated with FYM and composts showed a significant increase in TOC and BC in response to the increasing amounts of organic C added. Values of the BC/TOC ratio ranged from 1.4 to 2, without any significative differences among soil treatments. The qCO2 increased in the organic-amended soil and may have indicated microbial stress. The total amounts of metals in treated soils were lower than the levels permitted by the European Union in agricultural soils. DTPA-extractable metals increased in amended soils in response to organic C. A multiple regression analysis with stepwise selection of variables was carried out in order to discriminate between the influence exerted on DTPA-extractable metals by their total content, TOC and BC. Results showed that each metal behaved quite differently, suggesting that different mechanisms might be involved in metal bioavailability

Response of leguminosae to cadmium exposure

Abstract Bush bean and pea plants grown in a sandy substrate and treated daily with nutrient solutions containing either 50 and 125 pM cadmium (Cd), added as cadmium nitrate [Cd(NO3)2], were analyzed for dry matter production, total Cd content, and extractable Cd. Cadmium depressed dry matter production of both plant species. Bush bean plants accumulated larger amounts of Cd in tissues and displayed lower Cd tolerance than pea plants. The high accumulation of Cd in roots of bush bean does not seem to prevent Cd translocation. Pea plants show a higher exclusion capacity at the root level, suggesting that membrane selectivity rather than apoplastic compartmentation may act as a defence mechanism against Cd toxicity. Gel‐permeation chromatography and voltammetric analyses showed that part of water‐soluble Cd extracted from tissues of pea and bush bean was as free metal ion (Cd2+). In addition, Cd into the nutrient solution induced progressively the synthesis of water‐soluble proteins at low molecular weigth ...

Water- and pyrophosphate-extractable humic substances fractions as a source of iron for Fe-deficient cucumber plants

Abstract The capacity of Fe-deficient cucumber plants to utilise water-extractable and pyrophosphate-extractable humic substances as a source of Fe was investigated. Plants were grown for 13 days in nutrient solution in the presence or absence of Fe and during the last 7 days water-extractable and pyrophosphate-extractable humic substances were added to the solution at a final concentration of 5 μg organic C ml–1. The water-extractable humic fraction did not significantly modify leaf area and dry matter accumulation, leaf total Fe or chlorophyll content of cucumber plants adequately supplied with Fe. In contrast, pyrophosphate-extractable humic substances caused a slight but significant decrease of all the leaf parameters considered, with the exception of the chlorophyll content. Root Fe content of Fe-sufficient plants was decreased by more than 50% in the presence of each humified fraction. Addition of each humic fraction to Fe-deficient plants led to a partial disappearance of leaf chlorosis symptoms with a significant increase in chlorophyll and leaf Fe content. Fe content of roots was also significantly increased in Fe-deficient plants by the addition of humic substances to the nutrient solution. These results show that Fe-deficient cucumber plants can utilise Fe contained in the two fractions of humified organic matter. However, by calculating the amount of total Fe accumulated per plant in the presence of water-extractable or pyrophosphate-extractable humic substances, it could be seen that Fe contained in the water-extractable humic fraction was almost totally used by Fe-deficient cucumber plants, while that present in the pyrophosphate-extractable fraction could only be partially absorbed. The results strongly support a role of humified organic matter in Fe nutrition of plants and are discussed in terms of a possible interaction between soil humic substances and the biochemical mechanisms involved in the plant response to Fe deficiency.

Heavy metal bioaccumulation in lamb and sheep bred in smelting and mining areas of S.W. sardinia (Italy)

It is widely known that anthropogenic activities strongly contributed to heavy metals contamination of the environment. For this reason, distribution of heavy metals in soils and plants around urban and industrial point sources have been the object of extensive studies. Lesser attention has been given to accumulation of heavy metals in animals bred in these polluted environments, and relatively few works are concerned with the accumulation of heavy metals through the food chain. The aim of this work is to examine the distribution of heavy metals in two contaminated environments, a smelter-refinery and a mine area situated in S.W. Sardinia. The first sampling area is located near one of the most important Pb and Zn smelting-refineries of Europe, and the second near abandoned and working mines. In this study, target organs of sheep and lamb were considered for their heavy metals accumulation. Samples of vegetation were collected throughout the vegetative period and analyzed for their Pb, Zn and Cd content. Winter forage and soil were also sampled.

Analysis of intercellular cadmium forms in roots and leaves of bush bean

Abstract We characterized and quantified the chemical form of cadmium (Cd) in intercellular solutions of the apparent free space (AFS) of roots and leaves of bush bean plants. Plants were grown in sand and treated daily for five days with Hoagland nutrient solution containing, respectively, 0.5 and 1 mM Cd(NO3)2. The intercellular solution was collected by infiltration‐extraction procedure using successively distilled water, 5 mM CaCl2, and 5 mM EDTA in order to collect separately the water soluble, exchangeable, and complexed Cd. The ability of extradant solutions to remove Cd from the AFS of roots and leaves was: H2O < CaCl2 ≪ EDTA, confirming that most of Cd was bound at the cell wall. Voltarimetric technique showed that water‐soluble Cd in intercellular solutions of the root and leaf tissues was as the Cd2+ ion, suggesting that Cd might be taken up by the roots and transported to leaves as the free ion.

Characterization of organic matter from animal manures after digestion by earthworms

The humification index (HI) values of three different manures and earthworm casts were calculated for three different extractant solutions (0.5M sodium hydroxide, 0.1M sodium pyrophosphate pH 7 and 0.1M sodium pyrophosphate plus 0.1M NaOH). The alkaline sodium pyrophosphate solution was found to be the most suitable because of both its extraction efficiency and the quality of the organic matter extracted which allows a good characterization of the stabilization degree attained by composting. Neutral sodium pyrophosphate extracts also show characteristic HI values for different samples but lower extraction efficiencies. The HI values for sodium hydroxide extracts show only little differences between manures and composts. The good correspondence found between HI data and isoelectric focusing (IEF) patterns confirmed on one side that humification indexes give a quantitative measure of the humification degree, on the other side that IEF is a suitable technique in order to obtain qualitative informations on organic matter stabilization in earthworm casts.

Response of microbial biomass to air-drying and rewetting in soils and compost

The activity of microorganisms and the availability of composting substrates for decomposition are seriously affected by drying and rewetting cycles. We have measured microbial biomass C (BC) and ninhydrin reactive N (BNIN) of samples of composting material taken at different times from a pile of ligno-cellulosic wastes. Dynamics of these two parameters in control samples that were kept continuously moist were compared with those of samples of the same material that had been subjected to drying and rewetting. The study was also performed on soils to investigate analogies and differences of behaviour of microbial biomass in such different substrates. Moist samples from 10 soils with different organic C content (6.6–41.9 g kg−1 soil) were analyzed for their BC and BNIN content. The soils were then air-dried, rewetted and incubated at 25 °C for 10 days. On days 1, 3, 6 and 10 of incubation, samples were analyzed for BC and BNIN content. Compost samples from different composting stages of a mixture of cotton carding and yard wastes were air-dried, rewetted and incubated at 25 °C for 12 days, together with the corresponding moist samples (control). On days 1, 5 and 12 of incubation period, samples were analyzed for BC and BNIN content. The regression coefficient between BC and BNIN for all the compost data (continuously moist and rewetted) was 21.4 (r=0.89 P<0.001), very close to values normally found in soils, confirming the reliability of microbial biomass measurements performed on composting substrates. Soil drying caused on average a decrease in the size of microbial biomass with respect to moist samples of 13% for BC and 30% for BNIN. BC and BNIN of moist and rewetted soil samples were always significantly correlated. Microbial biomass content of rewetted compost samples up to 19 days from the beginning of the process were significantly different, but highly correlated with moist controls. No significant differences between moist and rewetted samples (RW) were found in samples collected during the maturing and curing phases. The different response to drying of soils and compost could be related to the greater increase of new available substrate in compost with respect to soil following the drying–rewetting treatment. Dynamics of BC/BNIN ratio in compost was coherent with the normal trend observed in the composition of microbial community during the process, from prevailing bacteria and actinomycetes to prevailing fungi.

Anomalous contents of heavy metals in soils and vegetation of a mine area in S.W. Sardinia, Italy

Samples of soils and vegetation from the mining area of South-West Sardinia (Italy) were analyzed for Pb, Zn, Cd, and Cu content. The area (more than 100 km2) is inhabited by many thousands of people; land utilization includes mainly grapes on some small plains and permanent sheep pasture on the hills. The levels of Pb, Zn, and Cd were found to be exceptionally high in most samples. Lead concentration was up to 71000 μg g−1 in the soils and 4000 jig g−1 in vegetation; Cd concentration was found up to 665 μg g−1 in soils and 26.5 μg g−1 in vegetation. The heavy metal content of some soil samples was highly variable. Data show that Pb is easily absorbed by plant roots and translocated to foliage. In spite of the high heavy metal level, no signs of toxicity were apparent in vegetation.

Temperature changes and the ATP concentration of the soil microbial biomass.

Abstract Two soils from temperate sites (UK; arable and grassland) were incubated aerobically at 0, 5, 15 or 25°C for up to 23 days. During this period both soils were analysed for soil microbial biomass carbon (biomass C) and adenosine 5′ triphosphate contents (ATP). Biomass C did not change significantly in either soil at any temperature throughout, except during days 0 to 1 in the grassland soil. Soil ATP contents increased slowly throughout the 23 days of incubation, from 2.2 to a maximum of 3.1 nmol ATP g −1 soil in the arable soil (a 40% increase) and from 6.2 to a maximum of 11.2 nmol ATP g −1 soil in the grassland soil (an increase of 81%), both at 25°C. Since biomass C did not change either with increasing temperature or increasing time of incubation, it was concluded that an increase in ATP was either due to an increase in adenylate energy charge or de novo synthesis of ATP, or both. During the incubation, biomass ATP concentrations ranged from about 5 to 12 μmol ATP g −1 biomass C but trends between biomass ATP and incubation temperatures were not very obvious until about day 13. On day 23, biomass ATP concentrations were positively and linearly related to temperature: (μmol ATP g −1 biomass C = 6.98 ± 0.35 + 0.134 ± 0.023 T 0 ( r 2 = 0.77) with no significant difference in the slope between the grassland and arable soils. At 25°C the biomass ATP concentration was 10.3 μmol g −1 biomass C, remarkably close to many other published values. It was concluded that, although the biomass increased its ATP concentration in response to increasing temperature, the increase was comparatively small. Also, at all temperatures tested, the biomass maintained its ATP concentration within the range commonly reported for micro-organisms growing expontentially in vitro. This is despite the fact that the biomass normally exhibits other features more typical of a “resting” or dormant population — a paradox which still is not resolved.