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Protein hydrolyzates (PHs) are a well-known group of plant biostimulants that are obtained by thermal, chemical, enzymatic or mixed hydrolysis from animal or plant sources. PHs are mainly applied to plants with the aim to improve their nutrition level, stimulate metabolism, and increase resistance to abiotic stress. Chemically, the PHs are a mixture of free amino acids, oligo- and polypeptides. Considering the differences in the source materials and hydrolytic processes used for their production it is not surprising that PHs are a very complex and inhomogeneous category of biostimulants. This is a critical point that should be considered by both manufacturers and potential users of such products. With the aim to identify a putative correlation among PHs physic-chemical properties, the different source materials and the hydrolytic process used for their production, 22 PHs available on the market were analyzed for: (i) total amino acids concentration, (ii) free amino acids concentration, (iii) degree of racemization, (iv) degree of hydrolysis and (v) apparent average molecular size. The obtained results confirmed the inhomogeneity PHs. However, the chosen parameters were able to provide information about the above-mentioned correlation. Total amino acids in particular were useful for the identification of the original source material. The degree of racemization was useful for the identification of the type of hydrolysis used during production (chemical or enzymatic). The degree of hydrolysis and free amino acid concentrations were useful for the identification of the intensity of the hydrolytic process. The average molecular size was useful for the identification of polydispersity of the peptide size. In conclusion, the PHs can be adequately characterized only through a multi-analytical approach. [ABSTRACT FROM AUTHOR]

In this study we provided information about the fate of hexavalent chromium (Cr(VI)) in soil and the effect exerted by Cr(VI) towards native soil microbial biomass. Our results indicate that soil attenuates the occurrence of Cr(VI) at a relatively fast rate - Cr(VI) reduction was almost complete in about two weeks. Microbial biomass size (microbial biomass carbon, MBC) and activity (as CO2-C evolution and enzymatic activities) were both affected by the presence of Cr(VI) in soil and did not fully recover concurrently with hexavalent chromium's complete disappearance. The addition of Cr(VI) to soil significantly reduced the arylsulphatase activity, which remained significantly impaired throughout the duration of the experiment and did not recover to initial values indicating its putative susceptibility towards the presence of Cr(III), too. β-glucosidase activity, on the other hand, was much less affected by presence of Cr(VI) in soil and the adverse effect of chromium did not persist over time. In conclusion, our findings suggest that Cr(VI) pollution has a prolonged negative effect on soil microbial pool that persists even after its disappearance. [ABSTRACT FROM AUTHOR]

In this study the influence of iron sulphate (FeSO4) on the dynamics of Cr(VI) - Cr(III) reduction in Cr(VI) spiked soil was evaluated, together with the concomitant assessment of the effect of the different treatments on soil microbial biomass size and activity. The results indicate that during the incubation period, the concentration of Cr(VI) in soil decreased over time, thus evidencing a natural attenuation capacity of soil towards chromate reduction. However, soil microbial biomass and respiration rate were both negatively affected by the presence of Cr(VI), and did not recover during the experiment. Soil amendment with FeSO4 increased the Cr(VI) reduction rate and mitigated its negative effect towards soil microbial biomass and activity. [ABSTRACT FROM AUTHOR]