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The use of halotolerant beneficial plant-growth-promoting (PGP) bacteria is considered as a promising eco-friendly approach to improve the salt tolerance of cash crops. One strategy to enhance the possibility of obtaining stress-alleviating bacteria is to screen salt impacted soils. In this study, amongst the 40 endophytic bacteria isolated from the roots of Sahara-inhabiting halophytes Atriplex halimus L. and Lygeum spartum L., 8 showed interesting NaCl tolerance in vitro. Their evaluation, through different tomato plant trials, permitted the isolate IS26 to be distinguished as the most effective seed inoculum for both plant growth promotion and mitigation of salt stress. On the basis of 16S rRNA gene sequence, the isolate was closely related to Stenotrophomonas rhizophila. It was then screened in vitro for multiple PGP traits and the strain-complete genome was sequenced and analysed to further decipher the genomic basis of the putative mechanisms underlying its osmoprotective and plant growth abilities. A remarkable number of genes putatively involved in mechanisms responsible for rhizosphere colonization, plant association, strong competition for nutrients, and the production of important plant growth regulator compounds, such as AIA and spermidine, were highlighted, as were substances protecting against stress, including different osmolytes like trehalose, glucosylglycerol, proline, and glycine betaine. By having genes related to complementary mechanisms of osmosensing, osmoregulation and osmoprotection, the strain confirmed its great capacity to adapt to highly saline environments. Moreover, the presence of various genes potentially related to multiple enzymatic antioxidant processes, able to reduce salt-induced overproduction of ROS, was also detected. [ABSTRACT FROM AUTHOR]

Aims: The Desert Locust (Schistocerca gregaria) occupies vast territories in the Saharan part of Africa. Its habitats have been described separately in several localities, yet a synthetic view is lacking. Previous researchers have provided lists of plants for each study site but rarely the corresponding information about their phytosociological context. The aim of this work was to give insights into the classes and alliances hosting the Desert Locust throughout the Saharo-Sindian and Saharo-Sahelian area. Location: We investigated four regions in the center and in the southern parts of Algerian Sahara, with altitudes ranging from 300 to 1050 m a.s.l. We also considered six localities taken from literature, of which two and four were selected in the Saharo-Sindian and Saharo-Sahelian regions respectively. Methods: We sampled 466 relevés between 2007 and 2013 to record the abundance-dominance of plants, and the density of Desert Locust. Sampling dates were adjusted to insect presence. The plant assemblages were defined by Ward's clustering method to obtain a balanced number of samples. The fidelity (phi coefficient) of plant species in the assemblages found was calculated. The link between Desert Locust density and different environmental parameters, including vegetation alliance proportions, was estimated through correlation analysis. Results: Hierarchical classification revealed 16 plant assemblages that do not clearly fit into the phytosociological system. Each assemblage contains species belonging to several alliances, highlighting the difficulty in defining plant associations in desert ecosystems. Desert Locust abundance was positively linked to the percentages of Saharo-Sindian plants and of the Antirrhino-Pithurantion scopariae alliance, but negatively so to plants associated with saline-gypsum soils. As with the Acacio-Panicion, the Antirrhino-Pithurantion scopariae is a desert steppe developed on oued edges (temporary river) but with a slightly higher annual rainfall. There is a set of stations, particularly near Bordj-Badji-Mokhtar, where the density of Desert Locust is not linked to preferred plants, suggesting that they constitute only survival biotopes. We also provide a wider view on the requirements of the Desert Locust to enter a gregarious phase, by including several literature stations of tropical Africa, in order to compare the different vegetation types. Even where the dominant vegetation remains the Acacio-Panicion, the flora is mainly Saharo-Sahelian and Sahelo-Sudanian, and not Mediterraneo-Saharo-Sindian. Conclusions: The habitat of Desert Locust is clearly defined by plant assemblages linked to the Acacio-Panicion alliance. There are significant differences between the vegetation associated with solitary and gregarious individuals. [ABSTRACT FROM AUTHOR]

Unpublished chemical and isotopic data taken in November 1992 from the three major Saharan aquifers, namely the Continental Intercalaire (CI), the Complexe Terminal (CT) and the phreatic aquifer (Phr), were integrated with original samples in order to chemically and isotopically characterize the largest Saharan aquifer system and investigate the processes through which groundwaters acquire their mineralization. Instead of classical Debye--Hückel extended law, a specific interaction theory (SIT) model, recently incorporated in PHREEQC 3.0, was used. Inverse modeling of hydrochemical data constrained by isotopic data was used here to quantitatively assess the influence of geochemical processes: at depth, the dissolution of salts from the geological formations during upward leakage without evaporation explains the transitions from CI to CT and to a first end member, a cluster of Phr (cluster I); near the surface, the dissolution of salts from sabkhas by rainwater explains another cluster of Phr (cluster II). In every case, secondary precipitation of calcite occurs during dissolution. All Phr waters result from the mixing of these two clusters together with calcite precipitation and ion exchange processes. These processes are quantitatively assessed by the PHREEQC model. Globally, gypsum dissolution and calcite precipitation were found to act as a carbon sink. [ABSTRACT FROM AUTHOR]

Abstract: The disequilibrium between 234U and 238U is commonly used as a tracer of groundwater flow. This paper aims to identify uranium contents and uranium isotopic disequilibria variation in groundwater sampled from deep Continental Intercalaire aquifer (southern Algeria and Tunisia). Large variations in both U contents (0.006–3.39ppb) and 234U/238U activity ratios (0.4–15.38) are observed. We conduct a first assessment in order to verify whether the results of our investigation support and complete previous hydrogeological and isotopic studies. The dissolved U content and 234U/238U activity ratio data were plotted on a two-dimensional diagram that was successfully utilized on sharing the CI aquifer into different compartments submitted to different oxidising/reducing conditions and leads also to distinguished two preferential flow paths in the Nefzaoua/Chott Fejej discharge area. Uranium isotopes disequilibrium indicate that ranium chemistry is mainly controlled by water–rock interaction enhanced by long residence time recognised for this aquifer. [Copyright &y& Elsevier]

Summary: The “Continental Intercalaire” from Sahara is one of the largest confined aquifers in the world. In the northern part of the basin, the depth of the aquifer ranges between 400 and 1800m and the main flow direction is from west to east. Chlorine-36 analyses were performed on groundwater samples mainly collected along this flowpath. They show a wide range of 36Cl contents, from 8 to 99×10−15 atat−1 expressed as 36Cl/Cl atomic ratio. In order to evaluate the epigene production, measurements were also performed on chloride extracted by leaching from a soil profile, near the recharge zone. This showed that the contribution of epigene production remains limited. A range of 36Cl/Cl ratios from 116 to 133×10−15 was adopted for groundwater recharging the aquifer, including both meteoric production and epigene production. For most of the samples collected along the main flowpath, a significant decay effect was observed. An attempt of dating was made by using an equation that takes into account radioactive decay of the meteoric–epigene input, deep production and chloride dissolution within the aquifer. The calculated 36Cl residence time varies from 16 to 500ka for the minimum ages, and from 25 to 1200ka for the maximum ages. An increase of residence time is observed up to about 500km from the recharge zone. This corresponds to mean flow velocities of 0.2–0.5ma−1 and to an average permeability of 1.1±0.6×10−5 ms−1, at the scale of several hundreds of kilometres. [Copyright &y& Elsevier]