On the radiative equilibrium of a stellar atmosphere. IV

In this paper the solution to the problem of line formation given in an earlier paper is obtained in its numerical form in the first three approximations. Tables for computing the residual intensity are given

Humic substances contribute to plant iron nutrition acting as chelators and biostimulants

Improvement of plant iron nutrition as a consequence of metal complexation by humic substances (HS) extracted from different sources has been widely reported. The presence of humified fractions of the organic matter in soil sediments and solutions would contribute, depending on the solubility and the molecular size of HS, to build up a reservoir of Fe available for plants which exude metal ligands and to provide Fe-HS complexes directly usable by plant Fe uptake mechanisms. It has also been shown that HS can promote the physiological mechanisms involved in Fe acquisition acting at the transcriptional and post-transcriptional level. Furthermore, the distribution and allocation of Fe within the plant could be modified when plants were supplied with water soluble Fe-HS complexes as compared with other natural or synthetic chelates. These effects are in line with previous observations showing that treatments with HS were able to induce changes in root morphology and modulate plant membrane activities related to nutrient acquisition, pathways of primary and secondary metabolism, hormonal and reactive oxygen balance. The multifaceted action of HS indicates that soluble Fe-HS complexes, either naturally present in the soil or exogenously supplied to the plants, can promote Fe acquisition in a complex way by providing a readily available iron form in the rhizosphere and by directly affecting plant physiology. Furthermore, the possibility to use Fe-HS of different sources, size and solubility may be considered as an environmental-friendly tool for Fe fertilization of crops

Response of barley plants to Fe deficiency and Cd contamination as affected by S starvation

Both Fe deficiency and Cd exposure induce rapid changes in the S nutritional requirement of plants. The aim of this work was to characterize the strategies adopted by plants to cope with both Fe deficiency (release of phytosiderophores) and Cd contamination [production of glutathione (GSH) and phytochelatins] when grown under conditions of limited S supply. Experiments were performed in hydroponics, using barley plants grown under S sufficiency (1.2mM sulphate) and S deficiency (0mM sulphate), with or without Fe III-EDTA at 0.08mM for 11d and subsequently exposed to 0.05mM Cd for 24h or 72h. In S-sufficient plants, Fe deficiency enhanced both root and shoot Cd concentrations and increased GSH and phytochelatin levels. In S-deficient plants, Fe starvation caused a slight increase in Cd concentration, but this change was accompanied neither by an increase in GSH nor by an accumulation of phytochelatins. Release of phytosiderophores, only detectable in Fe-deficient plants, was strongly decreased by S deficiency and further reduced after Cd treatment. In roots Cd exposure increased the expression of the high affinity sulphate transporter gene (HvST1) regardless of the S supply, and the expression of the Fe deficiency-responsive genes, HvYS1 and HvIDS2, irrespective of Fe supply. In conclusion, adequate S availability is necessary to cope with Fe deficiency and Cd toxicity in barley plants. Moreover, it appears that in Fe-deficient plants grown in the presence of Cd with limited S supply, sulphur may be preferentially employed in the pathway for biosynthesis of phytosiderophores, rather than for phytochelatin production

Characterization of humic fractions in leachates from soil under organic and conventional management and their interactions with the root zone

Humic fractions were shown to be closely involved in gene expression and promotion of different PM H+-ATPase isoforms, as well as in lateral root development, indicating an enhanced nutrient absorption capacity of the plant root system. HPLC-SEC confirmed that water-soluble humic substances (WSHS) correspond to a subfraction of the fulvic fraction of humic substances. This was supported by E465/E665 ratios higher than 8.5. These ratios generally increased over the growing season in cultivated soils but showed significant differences between conventionally and organically managed bare soils. FTIR data and the analytical quantification of carboxyls confirmed relevant structural changes in bare soil under both organic and conventional farming management. Absorption intensities ratios at 1,590–1,570 cm-1 and 1,440–1,380 cm-1 showed the predominant aliphatic character of these molecules

Characterization of humic fractions in leachates from soil under organic and conventional management and their interactions with the root zone

Humic fractions were shown to be closely involved in gene expression and promotion of different PM H+-ATPase isoforms, as well as in lateral root development, indicating an enhanced nutrient absorption capacity of the plant root system. HPLC-SEC confirmed that water-soluble humic substances (WSHS) correspond to a subfraction of the fulvic fraction of humic substances. This was supported by E465/E665 ratios higher than 8.5. These ratios generally increased over the growing season in cultivated soils but showed significant differences between conventionally and organically managed bare soils. FTIR data and the analytical quantification of carboxyls confirmed relevant structural changes in bare soil under both organic and conventional farming management. Absorption intensities ratios at 1,590\u20131,570 cm-1 and 1,440\u20131,380 cm-1 showed the predominant aliphatic character of these molecules

Copper and zinc as a window to past agricultural land-use.

Abstract Intensive agricultural management significantly affects soil chemical properties. Such impacts, depending on the intensity of agronomic practices, might persist for several decades. We tested how current soil properties, especially heavy metal concentrations, reflect the land-use history over a 24,000 ha area dominated by intensive apple orchards and viticulture (South Tyrol, ITA). We combined georeferenced soil analyses with land-use maps from 1850 to 2010 in a space-for-time approach to detect the accumulation rates of copper and zinc and understand how present-day soil heavy metal concentrations reflect land-use history. Soils under vineyards since the 1850s showed the highest available copper concentration (median of 314.0 mg kg-1, accumulation rate between 19.4 and 41.3 mg kg-1·10 y-1). Zinc reached the highest concentration in the same land-use type (median of 32.5 mg kg-1, accumulation rate between 1.8 and 4.4 mg kg-1·10 y-1). Using a random forest approach on 44,132 soil samples, we extrapolated land-use history on the permanent crop area of the region, reaching an accuracy of 0.72. This suggests that combining current soil analysis, historical management information, and machine learning models provides a valuable tool to predict land-use history and understand management legacies

Copper accumulation in vineyard soils: Rhizosphere processes and agronomic practices to limit its toxicity.

Viticulture represents an important agricultural practice in many countries worldwide. Yet, the continuous use of fungicides has caused copper (Cu) accumulation in soils, which represent a major environmental and toxicological concern. Despite being an important micronutrient, Cu can be a potential toxicant at high concentrations since it may cause morphological, anatomical and physiological changes in plants, decreasing both food productivity and quality. Rhizosphere processes can, however, actively control the uptake and translocation of Cu in plants. In particular, root exudates affecting the chemical, physical and biological characteristics of the rhizosphere, might reduce the availability of Cu in the soil and hence its absorption. In addition, this review will aim at discussing the advantages and disadvantages of agronomic practices, such as liming, the use of pesticides, the application of organic matter, biochar and coal fly ashes, the inoculation with bacteria and/or mycorrhizal fungi and the intercropping, in alleviating Cu toxicity symptoms

Plasmopara viticola infection affects mineral elements allocation and distribution in Vitis vinifera leaves

Plasmopara viticola is one of the most important pathogens infecting Vitis vinifera plants. The interactions among P. viticola and both susceptible and resistant grapevine plants have been extensively characterised, at transcriptomic, proteomic and metabolomic levels. However, the involvement of plants ionome in the response against the pathogen has been completely neglected so far. Therefore, this study was aimed at investigating the possible role of leaf ionomic modulation during compatible and incompatible interactions between P. viticola and grapevine plants. In susceptible cultivars, a dramatic redistribution of mineral elements has been observed, thus uncovering a possible role for mineral nutrients in the response against pathogens. On the contrary, the resistant cultivars did not present substantial rearrangement of mineral elements at leaf level, except for manganese (Mn) and iron (Fe). This might demonstrate that, resistant cultivars, albeit expressing the resistance gene, still exploit a pathogen response mechanism based on the local increase in the concentration of microelements, which are involved in the synthesis of secondary metabolites and reactive oxygen species. Moreover, these data also highlight the link between the mineral nutrition and plants\u2019 response to pathogens, further stressing that appropriate fertilization strategies can be fundamental for the expression of response mechanisms against pathogens