Giuseppe Concheri

Structural characteristics of humic substances as related to nitrate uptake and growth regulation in plant systems

Abstract Humic extracts with distinct chemical and physical-chemical characteristics, obtained by various soil extractants and from different sources, were used to study their biological activity. The humic structural features were related to the rate of nitrate uptake by barley seedlings and growth regulation in watercress and lettuce. Chemical analysis of functional groups, molecular weight distribution, and NMR quantitative spectra were used to characterize the humic extracts. Results showed that the most effective humic fraction on both plant nitrate uptake and hormone-like activity had the highest acidic functionality and the smallest molecular size, whereas both the aliphatic and aromatic content of extracts did not appear to play a role. Low molecular size fractions obtained from the original material by disaggregating the humic macromolecule through the formation of a sort of inverse micelle by acetic acid addition, showed results that confirmed the effectiveness of the combination of high acidity and low molecular size in influencing the biological activity of the plant system tested.

Soil organic matter mobilization by root exudates

In order to study the different soil organic matter mobilisation by agrarian (Zea mais: cultivars Paolo and Sandek) and forest (Picea abies Karst. and Pinus sylvestris L.) root exudates, three different soils (Dystric Spodic Cambisol--S1, Haplic Luvisol--S2 and Calcaric Cambisol--S3) have been considered. Treating the soils with water (control) or plant root exudates, soil organic matter extracts were obtained. The extracts were characterised by hormone-like activities and gas chromatographic/mass spectrometric (GC/MS) measurements. Water extract and plant root exudates exhibited no hormone-like activity, while the other soil-extracts were endowed with a different hormone-like behaviour. GC/MS data indicated that in the acid soils (S1) Sandek and Picea abies exudates showed a greater ability in extracting organic acid isomers (Cl4COOH, Cl5COOH and Cl7COOH), while in neutral soils (S3) all the exudates were active in separating organic acids. In intermediate conditions (S2), Picea abies and Pinus sylvestris exudates liberated C15COOH isomers, Paolo C11COOH isomers, while Sandek was not effective. The different role of plant root exudates in mobilising bio-molecules from the bulk of the soil is proposed.

Micelle-1ike conformation of humic substances as revealed by size exclusion chromatography

Abstract To gain further insight into the macromolecular behaviour of humic substances we treated a humic material with simple organic compounds and followed the change in molecular size distribution. Monocarboxylic, dicarboxylic, and tricarboxylic acids shifted the hunric absorbance from high to low molecular sizes in size exclusion chromatograms. Mineral acids, phenol, alcohols, were not able to produce the same shift and gave total absorbance at the column void volume as in the case of hunric substances alone. Our results are evidence of the micellar behaviour of humic substances in solution and of the importance of hydrophobic bondings in holding humic molecules together. The organic acids enter in the interior of the humic micelle and alter its stereochemical hydrophobic arrangement. In alkaline conditions, the developed negative charges disrupt the apparent high molecular size configuration and disperse the humic material into small-size micelles. This macromolecular property, that we report for the first time, may be of great importance in understanding the biological activity and the overall environmental behaviour of humic substances.

Biological Activity of Humus

Publisher Summary The addition of organic manure maintains and even improves soil fertility. Humus is recognized as one of the major natural resources for agricultural purposes. Positive effects of humic substances (HS) on plant growth demonstrate that in rye plants humic substances have a greater effect on root development than on leaf and stem development. Similar studies carried out with the humic substances labeled with 14C, established whether the positive effect of these substances was only through an indirect effect, that is, superficial physical contact, or direct effect wherever the substances were absorbed and translocated into the plant. Labeled humic substances, above all those with low MW (molecular weight), show their ability to be absorbed by the plant and be translocated into the plant. Integrating inorganic fertilizers with lower energy organic inputs has become evident not just for economical reasons but for environmental questions as well. The chapter describes the necessity to reconsider the indiscriminate use of chemical resources in modern agriculture and to recycle organic wastes, which can affect crop growth and productivity.

Nitrate uptake and atpase activity in oat seedlings in the presence of two humic fractions

Abstract HEf is a water-soluble humic constituent of molecular size compatible with uptake by plant roots. In naturally-occurring humic material, HEf is usually encased in macrostructured, high-molecular-weight, humic constituents (HSp) without biological activity. One prerequisite for any direct biological action by humic substances is therefore dissociation of the HEf-HSp structure. In order to investigate the above interaction, the effects of HEf and HSp on nitrate uptake and microsomal (Mg2+ K+) ATPase activity in oat roots were studied. HEf stimulated nitrate uptake with a peak value at 1.0 mg Cl−1, K+-stimulated ATPase activity of oat root microsomes, and H+ extrusion from roots, but it decreased ATP concentrations and did not influence O2 consumption. In contrast. HSp inhibited NO−3 transport at concentrations higher than 0.5 mg Cl−1, and showed only negligible effects on the considered variables. These results suggest that HEf stimulates NO−3 transport by activating K+-stimulated ATPase, whose activity lowered the ATP content of the cell. These effects are probably due both to the surfactant behaviour of humic substances (critical micelle concentration is 0.25 mg C ml−1 for HEf and 0.36 mg C ml−1 for HSp) and to their biological activity.

Effect of earthworm humic substances on esterase and peroxidase activity during growth of leaf explants of Nicotiana plumbaginifolia

SummaryLeaf explants of Nicotiana plumbaginifolia were compared in cultures supplemented with hormones or humic substances (extracted from faeces of Allolobophora caliginosa) of various molecular complexity and concentration. The results showed that the humic substances (F1, F2, and T) at the concentration of 1 mg C l-1 produced greater leaf explants than those grown in the control. Furthermore, humic fractions like gibberellic alone induced a rhizogenic activity in leaf explants. Quantitative differences were also observed in the peroxidase activity induced in Nicotiana plumbaginifolia by humic matter (F2, F2, and T). In addition, the Nicotiana sp. tissue treated with humic fractions revealed, in the esterase enzyme pattern, the appearance of the 2a band, which was attributable to indoleacetic acid, since its profile was consistent with those obtained from tissues treated with indoleacetic acid. These differences demonstrate that humic substances exhibited a hormone-like behaviour, but no evidence of a relationship between biological activities and chemical characteristics of humus substances was found.

Effect of molecular complexity and acidity of earthworm faeces humic fractions on glutamate dehydrogenase, glutamine synthetase, and phosphoenolpyruvate carboxylase in Daucus carota α II cells

Carrot cells were grown in cultures supplemented with two hormones [2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzylaminopurine (6BAP)] and two humic fractions extracted from earthworm faeces, one with high acidity and a low apparent molecular size (<3500) and the other with low acidity and a large molecular size. 2,4-D stimulated growth through an effect on cell enlargement, while the strongly acidic humic fraction (0.2 mg l-1) and the weakly acidic fraction (1 mg l-1) were both less effective. With 4–16 h of pre-incubation, the highly acid humic fraction, mainly alone, induced the best increase in protein content; the effect of the weakly acid humic fraction and the hormones was generally less important. The two humic fractions also differed in their influence on glutamate dehydrogenase activity. After 2 h of pretreatment, the highly acidic fraction increased glutamate dehydrogenase activity, while the other fraction did not affect it. After 4–16 h of pre-incubation, the activity of this enzyme was still not influenced by these humic fractions. The presence of the two hormones did not interfere with the humic matter effects. Glutamine synthetase activity was not affected by a pre-incubation of up to 4 h with the two humic fractions, but it was stimulated after 8–16 h of pre-incubation. A 2,4-D+6BAP mixture stimulated glutamine synthetase activity (from +12 to +50%). Again, the presence of the hormones did not interfere with the effects induced by the humic fractions. After 16 h of pre-incubation, phosphoenolpyruvate carboxylase activity was increased by the highly acidic humic fraction (+93%) and by both humic fractions together (+34%). An explanation of the different incubation times necessary for the humic fractions to exert stimulatory effects on these enzymes is proposed here. The regulatory properties of the strongly acidic humic fraction appeared to depend on the combination of high acidity (expecially carboxylic C) with low molecular size.

Soil humic compounds and microbial communities in six spruce forests as function of parent material, slope aspect and stand age

The influences on soil chemical and microbial properties of parent material, north south aspect and time measured as stand age were investigated in six spruce (Picea abies (L.) Karst.) forests located in the alpine range of Northern Italy. Soil samples from A horizons were analysed for humic substances and in parallel Amplified Ribosomal DNA Restriction Analysis (ARDRA) community profiles and microbial biomass carbon and nitrogen content were determined. Chemical data were analyzed by canonical discriminant analysis while the ARDRA fingerprints were ordered in clusters using image analysis software. The geologic parent material was the most determining factor and the aspect-dependent microclimate features also played a distinct role in defining both soil chemistry and microbial community composition; in contrast the composition of the deeper humus layers (OH, A) was stable and similar within a spruce forest cycle time. Most important variables in the construction of the discriminating models resulted soil pH, Dissolved Organic Carbon content and Dissolved Organic Matter phenolic compounds. Bacterial communities appeared to be shaped first and foremost by the substratum, secondly by mountain slope orientation, and thirdly by forest stage, thus confirming the CDA model.

Accumulation and Distribution Pattern of Macro- and Microelements and Trace Elements in Vitis vinifera L. cv. Chardonnay Berries

This paper describes the accumulation pattern of 42 mineral elements in Vitis vinifera L. berries during development and ripening and their distribution in berry skin, seeds, and flesh around harvest time. Grape berries were sampled in two different vineyards with alkaline soil and analyzed using a ICP-MS. Although elemental amounts were significantly different in the grapes from the two vineyards, the accumulation pattern and percentage distribution in different parts of the berries were generally quite similar. Ba, Eu, Sr, Ca, Mg, Mn, and Zn accumulate prior to veraison. Al, Ce, Dy, Er, Ga, Gd, Ho, La, Nd, Pr, Sm, Sn, Zr, Th, Tm, U, Y, and Yb accumulate mainly prior to veraison but also during ripening. Ag, As, B, Cd, Cs, Cu, Fe, Ge, Hg, K, Li, Na, P, Rb, Sb, Se, and Tl accumulate progressively during growth and ripening. With regard to distribution, Ba, Ca, Eu, Fe, Mn, P, Sr, and Zn accumulate mainly in the seeds, Al, B, Ga, Sn, and the rare earths analyzed, except for Eu, accumulate mainly in the skin, and Ag, As, Cd, Cs, Cu, Ge, Hg, K, Li, Mg, Na, Rb, Sb, Se, Th, Tl, U, and Zr accumulate mainly in the flesh. A joint representation of the accumulation and distribution patterns for the elements in the berry is also given.

Chemical elemental distribution and soil DNA fingerprints provide the critical evidence in murder case investigation

Background The scientific contribution to the solution of crime cases, or throughout the consequent forensic trials, is a crucial aspect of the justice system. The possibility to extract meaningful information from trace amounts of samples, and to match and validate evidences with robust and unambiguous statistical tests, are the key points of such process. The present report is the authorized disclosure of an investigation, carried out by Attorney General appointment, on a murder case in northern Italy, which yielded the critical supporting evidence for the judicial trial. Methodology/Principal Findings The proportional distribution of 54 chemical elements and the bacterial community DNA fingerprints were used as signature markers to prove the similarity of two soil samples. The first soil was collected on the crime scene, along a corn field, while the second was found in trace amounts on the carpet of a car impounded from the main suspect in a distant location. The matching similarity of the two soils was proven by crossing the results of two independent techniques: a) elemental analysis via inductively coupled plasma mass spectrometry (ICP-MS) and optical emission spectrometry (ICP-OES) approaches, and b) amplified ribosomal DNA restriction analysis by gel electrophoresis (ARDRA). Conclusions Besides introducing the novel application of these methods to forensic disciplines, the highly accurate level of resolution observed, opens new possibilities also in the fields of soil typing and tracking, historical analyses, geochemical surveys and global land mapping.