No abstract

Certain species of plants can benefit from synergistic effects with plant growth-promoting rhizobacteria (PGPR) that improve plant growth and metal accumulation, mitigating toxic effects on plants and increasing their tolerance to heavy metals. The application of PGPR as biofertilizers and atmospheric nitrogen fixators contributes considerably to the intensification of the phytoremediation process. In this paper, we have built a system consisting of rhizospheric Azotobacter microbial populations and Lepidium sativum plants, growing in solutions containing heavy metals in various concentrations. We examined the ability of the organisms to grow in symbiosis so as to stimulate the plant growth and enhance its tolerance to Cr(VI) and Cd(II), to ultimately provide a reliable phytoremediation system. The study was developed at the laboratory level and, at this stage, does not assess the inherent interactions under real conditions occurring in contaminated fields with autochthonous microflora and under different pedoclimatic conditions and environmental stresses. Azotobacter sp. bacteria could indeed stimulate the average germination efficiency of Lepidium sativum by almost 7%, average root length by 22%, average stem length by 34% and dry biomass by 53%. The growth of L. sativum has been affected to a greater extent in Cd(II) solutions due its higher toxicity compared to that of Cr(VI). The reduced tolerance index (TI, %) indicated that plant growth in symbiosis with PGPR was however affected by heavy metal toxicity, while the tolerance of the plant to heavy metals was enhanced in the bacteria-plant system. A methodology based on artificial neural networks (ANNs) and differential evolution (DE), specifically a neuro-evolutionary approach, was applied to model germination rates, dry biomass and root/stem length and proving the robustness of the experimental data. The errors associated with all four variables are small and the correlation coefficients higher than 0.98, which indicate that the selected models can efficiently predict the experimental data.

The paper is a short review on the soil decontamination applying ex-situ techniques. Some sources and pathways of soil contamination are discussed. It was revealed that available techniques for soil decontamination can be divided in two parts, depending on where the action have place: in-situ or ex-situ. Also, depending on the nature of the process, these techniques can be biological, physical-chemical and thermal. In order to decontaminate soils properly, the primary contaminants (hydrocarbons such as petroleum residues, solvents, pesticides, herbicides, wood preservatives, heavy metals, munitions, which result from different industries and agricultural activities) have to be detected and analyzed. The main features of ex-situ soil decontamination are reviewed and also status of each technology, advantages, disadvantages, limitations, and contaminants treated, are included.

No abstract

The stability of soil aggregates is an indicator of soil structure. Soil acidity affects soil structure stability. Soil acidity has two components: active acidity and exchangeable acidity. In natural conditions, each soil type has a certain level of acidity, which is given by its composition, natural vegetation, the chemical composition of precipitations and other factors that cause changes over time in soil pH. Acidic soils are characterized by physical, chemical and biological properties adverse to crop development. The main objective of the research was to establish a correlation between exchangeable acidity and soil structure stability. Experimental research was conducted on 16 soil types, which are characteristic to North Moldova and Bucovina, Romania's provinces. The total cation exchange capacity (T) of this soils is between 11.11 and 53.20 me/100g and the exchange bases sum (SB) varies from 0.70 to 31.92 me/100g. The correlations between Is (water stability index of soil structure) and H + /T are given by linear regression and by regression straight intervals with variable slope. Researchers have shown that to a variation of H + /T ratio between 0.0-0.6, aggregate stability more pronounced decrease with increasing concentration of H + exchangeable ions in the soil, compared with the range 0.8-1 of the ratio. In the second range, the influence of increasing concentration of exchangeable H + ions on the stability of soil structure is less pronounced.