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This study investigated the seed priming effects with aqueous extracts from the cyanobacterium Anabaena minutissima(AM) and the brown seaweed Sargassum vulgare(SV) on the growth and nutritional properties of China Rose (CR), Daikon (D), and Sango Red (SR) radish varieties. AM and SV biomasses were chemically analyzed. FTIR spectra of biomasses exhibited functional groups characteristic of amides I and II of proteins in AM and functional groups associated with the pyranose ring of carbohydrates in SV. The extracts differed in total proteins, phycobiliproteins, carbohydrates, chlorophylls, carotenoids, and antioxidant activity. Seed priming with AM and SV particularly increased seed germination (2% in CR), moisture (5% in D with AM), sprout weight (35% with AM), and height (12% with SV). In the elemental analysis of sprouts, Na, Ca, and Mg levels increased variably across all varieties of both extracts. Principal component analysis revealed significant separation among treatments in SR and D varieties, confirming the effectiveness of the seed priming.

The adsorption of humic substances on Ag nanoparticles (AgNPs) is of crucial environmental importance and determines the toxicity of these NPs and the structure of adsorbed organic matter. In this work, the adsorption of two standard soil and leonardite International Humic Substances Society humic acids was studied on AgNPs of different sizes, shapes (spherical and star-like), and interfacial chemical compositions. Surface-enhanced optical (Raman and fluorescence) spectroscopies were used to follow the specific chemical groups involved in this adsorption. By means of the latter optical techniques, information regarding the binding mechanism and the macromolecular aggregation can be deduced. The influence of the surface chemical composition induced by the different functionalizations of the interfaces of these NPs is highly important regarding the chemical interactions of these complex organic macromolecules. The surface functionalization with positively charged alkyl diamines led to a large increase in the adsorption as well as a strong structural rearrangement of the macromolecule once adsorbed onto the surface.

•High phosphorus values identify the samples from a droveway from Bronze Age.•δ13C values of the ancient road were close to the typical values of terrestrial animals.•The fatty acids in the samples suggested the presence of fats from ruminant animals.•A multiparametric chemical approach is useful in archaeology.

Carbon stabilization in soil aggregates has been proposed as an important mechanism for carbon sequestration in agricultural soils. However, few studies have investigated how long‐term strategies for accumulating C in the soil (e.g., organic fertilizers) can affect humic substance composition in aggregate‐size fractions. The aim of this work was to investigate the effects of long‐term application of farmyard manure (FYM) and mineral (MIN) fertilization on the humic carbon (HC) chemical structure extracted from macroaggregates (MA) (2000–250μm), microaggregates (MI) (53–250 μm) and silt–clay (SC) (<53 μm) fractions of two different soils (clay and peaty) by using δ13C, solid‐state 13C cross‐polarization‐magic angle spinning nuclear magnetic resonance (CP MAS 13C NMR) and diffuse reflectance infrared Fourier transform (DRIFT) analyses. Results showed that FYM had improved the HC concentration compared with the unfertilized and MIN fertilization. In clay soil, MIN fertilization led to a significantly heavier isotope 13C enrichment in the SC than macro‐ and microaggregate fractions, suggesting that HC in this fraction was the oldest and most stabilized. This was not so evident in peaty soil, where the HC was probably in an early stage of the humification process. In addition, the HC structure changed in both soils as a consequence of the treatments. The FYM amendment caused a decrease in O, N‐alkyl‐C, and alkyl C from macroaggregate to SC fractions, suggesting an advanced state of humic component degradation. However, FYM led to a considerably positive effect on the aromatic C content in both soils. This effect was magnified in the microaggregates of clay soil. These results revealed that the structural changes of HC in different soil aggregates make it possible to understand the effects of mineral and organic fertilization on cultivated soils.

Humic substances (HS) represent the organic material mainly widespread in nature. HS have positive effects on plant physiology by improving soil structure and fertility and by influencing nutrient uptake and root architecture. The biochemical and molecular mechanisms underlying these events are only partially known. HS have been shown to contain auxin and an “auxin-like” activity of humic substances has been proposed, but support to this hypothesis is fragmentary. In this review article, we are giving an overview of available data concerning molecular structures and biological activities of humic substances, with special emphasis on their hormone-like activities.

To understand if the biological activity of humic substances may be related to their molecular weight or chemical structure, two humic substances, derived from an Ah horizon of uncultivated couch grass [Elytrigia repens(L.) Desv. ex Nevski] and an Ah horizon of forest soil, were extensively characterized by means of different spectroscopic techniques (diffuse reflectance infrared Fourier transform [DRIFT] and 1H nuclear magnetic resonance [NMR]). The two humic substances, each separated in fractions with low (<3500 Da) and high (>3500 Da) relative molecular mass were compared for their effects on Pinus nigraJ.F. Arnold callus. Growth of callus, the soluble sugar content, free amino acid pool, and the activities of the key enzymes involved in C and N metabolism were investigated. Callus was grown for a subculture period (28 d) on basal Murashige and Skoog medium plus humic matters with or without different hormones: indole‐3‐acetic acid, 2,4‐dichlorophenoxyacetic acid, or 6‐benzylaminopurine. The results of 1H‐NMR spectra and the DRIFT spectroscopy showed significant differences in the chemical composition between forest and grass humic substances. A large amount of aliphatic and H‐sugarlike component and an intense chemical shift of the β‐CH3region in both grass humic fractions were observed, while high contents of betaine, organic acid, and COOH groups in both forest humic fractions were detected. A different biological activity between the grass and forest humic fractions was also observed. Thus, the different activity of the two humic substances used seems related to the diverse chemical composition rather than to different molecular weights.

Abstract:  The effects of two humic acid extractants, 0.1 M Na4P2O7 plus 0.1 M NaOH (NaPP) and 0.1 M NaOH (NaOH), on the activity and stability of a humic-urease complex were studied. The two humic acids isolated (HANaPP and HANaOH) exhibited different elemental compositions, metal concentrations and structural modifications in the FT-IR spectra. Depending on the pH, HANaPP and HANaOH influenced both the urease activity and urease kinetic parameters (V max and K m) in the same way. They inhibited urease activity between pH 6 and 7 and reduced the V max of the reaction at pH 6 and 7. The presence of humic acids improved the affinity of the enzyme for the substrate (K m). The stability of the urease with time, and in the presence of pronase, was improved by HANaPP and HANaOH with respect to free enzyme. These results confirm the importance of the interaction of urease with humic acids as a fundamental gateway for extracellular urease stabilisation. Since no difference in the extent of urease inhibition and urease stabilisation was observed for the two humic acids, it may be concluded that neither urease activity nor stability are influenced by the humic acid extractant used.

FT-IR, FT-Raman, and 1H-NMR spectroscopies were applied to investigate molecular changes in soil organic matter (SOM) treated with different biomasses. The experiment consisted of several plots of soil treated over a 22-year period (from 1972 to 1994) with different amendments: cattle manure (CM), cow slurries (CS), and crop residues (CR). Samples taken from these plots were analyzed and compared with the unamended soil (C), which was used as the control sample. The samples were analyzed for both total organic carbon (TOC) and total nitrogen (N) content, both at the beginning of the study and after 22 years of treatments. The plots amended with CS and CR and the unamended plots showed a decrease in TOC and N after 22 years when compared with the control at the beginning of the experiment. However, the amended soil with CM showed a linear increase in TOC and N in relation to the control.