Patrizia Zaccheo

The effect of commercial humic acid on tomato plant growth and mineral nutrition

Abstract The effects of humic acids extracted from two commercially‐available products (CP‐A prepared from peat and CP‐B prepared from leonardite) on the growth and mineral nutrition of tomato plants (Lycopersicon esculentum L.) in hydroponics culture were tested at concentrations of 20 and 50 mg L‐1. Both the humic acids tested stimulated plants growth. The CP‐A stimulated only root growth, especially at 20 mg L‐1 [23% and 22% increase over the control, on fresh weight basis (f.w.b.), and dry weight basis (d.w.b.), respectively]. In contrast, CP‐B showed a positive effect on both shoots and roots, especially at 50 mg L‐1 (shoots: 8% and 9% increase over the control; roots: 18% and 16% increase over the control, on f.w.b. and d.w.b., respectively). Total ion uptake by the plants was affected by the two products. In particular, CP‐A showed an increase in the uptake of nitrogen (N), phosphorus (P), iron (Fe), and copper (Cu), whereas, CP‐B showed positive effects for N, P, and Fe uptake. The change in the F...

Ammonium nutrition as a strategy for cadmium mobilisation in the rhizosphere of sunflower

Ammonium nutrition of higher plants results in rhizosphere acidification due to proton excretion by root cells. The acidification induced by ammonium-fed plants can be exploited to promote a localised metal mobilisation in neutral to alkaline polluted soils and therefore to improve phytoextraction. The effects of ammonium uptake by sunflower (Helianthus annuus L.) plants on the external medium pH, aerial and root growth and tolerance to soluble Cd were studied in hydroponic culture. The ammonium-fed sunflowers induced a strong acidification of the solution and, compared to the nitrate-fed sunflowers, a small modification in mineral nutrition and a different Cd partitioning between root and shoot. Moreover, ammonium nutrition was found to induce a great mobilisation of a sparingly soluble form of cadmium (CdCO3). A pot experiment studied the ability of different ammonium-based fertilisers (ammonium sulphate, ammonium thiosulphate, urea) to modify bulk and rhizo-soil pH, compared to the effect of calcium nitrate and to the unfertilised soil. Furthermore, in order to promote the persistence of ammonium in soil, a combined treatment of ammonium sulphate and DMPP, a nitrification inhibitor, was tested. Soil pH was strongly modified by chemical and biological processes involved in fertiliser transformations. In particular, due to nitrification, all ammonium-based treatments showed a bulk soil acidification of over 1.5 pH units and a relative increase in rhizo-soil pH as a consequence of nitrate uptake. The treatment with DMPP showed an opposite trend with a lower pH in rhizo-soil than in bulk soil. The ability of ammonium-fed plants to mobilise heavy metals from the non-labile pool was studied in another pot experiment using three soils with different properties and at different degree and type of heavy metal contamination. Whatever the soil, the metal concentrations in shoots were higher in plants fed with ammonium (ammonium sulphate plus DMPP treatment). Our results support the hypothesis that ammonium nutrition with nitrification inhibitors is a viable strategy to improve heavy metals phytoextraction while protecting bulk soil from acidification and presumably from metal leaching.

Microbial transformations of arsenic: perspectives for biological removal of arsenic from water

Arsenic is present in many environments and is released by various natural processes and anthropogenic actions. Although arsenic is recognized to cause a wide range of adverse health effects in humans, diverse bacteria can metabolize it by detoxification and energy conservation reactions. This review highlights the current understanding of the ecology, biochemistry and genomics of these bacteria, and their potential application in the treatment of arsenic-polluted water.

Decomposition of organic residues in soil: experimental technique and spectroscopic approach

Abstract DRIFT (diffuse reflectance infrared Fourier-transform) spectroscopy was used to follow the early transformations that take place after the incorporation of organic materials in soil. Alfalfa (A), dried maize (DM), laboratory-composted maize (CM), and two commercial composts (YWC and MWC) confined into fiberglass bags were incubated in sand with and without planting with lettuce. DRIFT spectra of these materials before and after incubations were correlated with CO 2 -C evolution and mass, carbon and nitrogen balances. Spectra obtained by successive subtractions allowed us to distinguish between the main classes of biochemical compounds (cellulose, lignin, polypeptides, pectins) and to study their degradation during incubation. Quantitative spectroscopic determination of lignin showed a relative enrichment in the incubated materials. This experimental approach can be applied to studies on the degradation pathway of green manure materials like A, DM and CM but seems less appropriate for commercial composts.

Nitrogen transformation in soil treated with 15N labelled dried or composted ryegrass

A 5-month laboratory incubation experiment was conducted to study the immobilization-mineralization of N in soil to which dried or composted 15N labelled ryegrass (Lolium italicum L.) had been added. Cellulose was added to dried ryegrass to give a C/N ratio similar to that of composted ryegrass. Exchangeable NH4+ and NO3−, HCl-hydrolyzable N forms, microbial biomass N, NaOH-soluble and insoluble N were monitored during incubation. Dried ryegrass brought about a significant increase in total and labelled exchangeable NH4+, while a rapid immobilization and a subsequent slow release of exchangeable NH4+ was observed in soil with composted ryegrass, together with a resistance to degradation of the labelled humic substances. Compounds synthesized during the composting process and resistant to microbial decomposition probably caused an increase in the amino-acid fraction of soil. These findings suggest that composting can reduce the risk of N losses.

Arsenic transforming abilities of groundwater bacteria and the combined use of Aliihoeflea sp. strain 2WW and goethite in metalloid removal

Several technologies have been developed for lowering arsenic in drinking waters below the World Health Organization limit of 10 μg/L. When in the presence of the reduced form of inorganic arsenic, i.e. arsenite, one options is pre-oxidation of arsenite to arsenate and adsorption on iron-based materials. Microbial oxidation of arsenite is considered a sustainable alternative to the chemical oxidants. In this contest, the present study investigates arsenic redox transformation abilities of bacterial strains in reductive groundwater from Lombardia (Italy), where arsenite was the main arsenic species. Twenty isolates were able to reduce 75 mg/L arsenate to arsenite, and they were affiliated to the genera Pseudomonas, Achromobacter and Rhodococcus and genes of the ars operon were detected. Three arsenite oxidizing strains were isolated: they belonged to Rhodococcus sp., Achromobacter sp. and Aliihoeflea sp., and aioA genes for arsenite oxidase were detected in Aliihoeflea sp. strain 2WW and in Achromobacter sp. strain 1L. Uninduced resting cells of strain 2WW were used in combination with goethite for arsenic removal in a model system, in order to test the feasibility of an arsenic removal process. In the presence of 200 μg/L arsenite, the combined 2WW-goethite system removed 95% of arsenic, thus lowering it to 8 μg/L. These results indicate that arsenite oxidation by strain 2WW combined to goethite adsorption is a promising approach for arsenic removal from contaminated groundwater.

The role of manure in the management of phosphorus resources at an Italian crop-livestock production farm

A quantitative knowledge of P cycling in dairy farms during a production cycle is the basis for optimizing fertilizer P management, because utilization of P by farm animals and its transfer to barn products are incomplete; animal manure represents a valuable source of P to sustain crop requirements. The nutrient content of manure is always difficult to determine precisely, because of the variability and fluctuation in daily water content and composition. Estimates of the P content of each material that moves to, from and within a dairy farm located in Lombardy were determined for one year by collecting farm data, sampling and analyzing farm materials (feeds, beddings, milk, hays and silage, etc.) and estimating through model calculation P retained in animals and in farm wastes. Two subcycles were investigated: the barn subcycle and the soil-crop subcycle, connected together by wastes, grasses and corn silage. The overall P balance in the farm studied with total stocking of 1.1 t of liveweight/ha, indicated a high manure potential for crop-needs that excludes use of inorganic P fertilizers. Moreover, detailed analysis of the various P pools has shown the relative contribution of each component to P cycling at the farm.

Chromium ions toxicity on the membrane transport mechanism in segments of maize seedling roots

Abstract Chromium ions affect the proton extrusion and the potassium uptake capacity in segments of maize seedling roots. The hypothesis that these effects can explain the chromium ions toxicity in plants is discussed.

Effectiveness of various sorbents and biological oxidation in the removal of arsenic species from groundwater

Environmental context Arsenic contamination of aquifers is a worldwide public health concern and several technologies have been developed to reduce the arsenic content of groundwater. We investigated the efficiency of various materials for arsenic removal from groundwater and found that iron-based sorbents have great affinity for arsenic even if groundwater composition can depress their ability to bind arsenic. Moreover, we showed that the use of microorganisms can enhance the removal of arsenic from groundwater. Abstract The AsIII and AsV adsorption capacity of biochar, chabazite, ferritin-based material, goethite and nano zero-valent iron was evaluated in artificial systems at autoequilibrium pH (i.e. MilliQ water without adjusting the pH) and at approximately neutral pH (i.e. TRIS-HCl, pH 7.2). At autoequilibrium pH, iron-based sorbents removed 200μgL–1 As highly efficiently whereas biochar and chabazite were ineffective. At approximately neutral pH, sorbents were capable of removing between 17 and 100% of AsIII and between 3 and 100% of AsV in the following order: biochar<chabazite<ferritin-based material<goethite<nano zero-valent iron. Chabazite, ferritin-based material and nano zero-valent iron oxidised AsIII to AsV and ferritin-based material was able to reduce AsV to AsIII. When tested in naturally As-contaminated groundwater, a marked decrease in the removal effectiveness occurred, due to possible competition with phosphate and manganese. A biological oxidation step was then introduced in a one-phase process (AsIII bio-oxidation in conjunction with AsV adsorption) and in a two-phase process (AsIII bio-oxidation followed by AsV adsorption). Arsenite oxidation was performed by resting cells of Aliihoeflea sp. strain 2WW, and arsenic adsorption by goethite. The one-phase process decreased As in groundwater to 85%, whereas the two-phase process removed up to 95% As, leaving in solution 6μgL–1 As, thus meeting the World Health Organization limit (10μgL–1). These results can be used in the scaling up of a two-phase treatment, with bacterial oxidation of As combined to goethite adsorption.

Effect of zinc on nitrogen transformation during composting process and in soil

The influence of Zn on nitrogen partitioning in different organic fractions during plant composting and on nitrogen transformation in compost amended soil added with ammonium sulphate, was investigated. 15N labelled maize plants (stems and leaves) were composted with and without high level of ZnSO4 so obtaining a Zn enriched compost, (4000 mg kg−1 of Zn), and a low Zn compost (control compost). The carbon and nitrogen recovery in the alkali insoluble, alkali soluble-acid insoluble and alkali and acid soluble fractions showed that two different end-products were obtained. In fact the presence of Zn induced a decrease on the rate of carbon compounds humification and the lowering of alkali insoluble nitrogen level.