Biotic and abiotic factors shape arbuscular mycorrhizal fungal communities associated with the roots of the widespread fern Botrychium lunaria (Ophioglossaceae).

Arbuscular mycorrhizal fungi (AMF) play central roles in terrestrial ecosystems by interacting with both above and belowground communities as well as by influencing edaphic properties. The AMF communities associated with the roots of the fern Botrychium lunaria (Ophioglossaceae) were sampled in four transects at 2400 m a.s.l. in the Swiss Alps and analyzed using metabarcoding. Members of five Glomeromycota genera were identified across the 71 samples. Our analyses revealed the existence of a core microbiome composed of four abundant Glomus operational taxonomic units (OTUs), as well as a low OTU turnover between samples. The AMF communities were not spatially structured, which contrasts with most studies on AMF associated with angiosperms. pH, microbial connectivity and humus cover significantly shaped AMF beta diversity but only explained a minor fraction of variation in beta diversity. AMF OTUs associations were found to be significant by both cohesion and co-occurrence analyses, suggesting a role for fungus-fungus interactions in AMF community assembly. In particular, OTU co-occurrences were more frequent between different genera than among the same genus, rising the hypothesis of functional complementarity among the AMF associated to B. lunaria. Altogether, our results provide new insights into the ecology of fern symbionts in alpine grasslands.

Comparison of the plant growth-promotion performance of a consortium of Bacilli inoculated as endospores or as vegetative cells.

The effect of three plant growth-promoting Bacillus strains inoculated either alone or as a consortium was tested on oat (Avena sativa) growth. The bioinoculants were applied as vegetative cells or endospores at low cell densities on the seeds and their effect was tested in sterile in vitro conditions, pot experiments, and a field trial. The in vitro seed germination assay showed that both individual bacterial inocula and bacterial consortia had positive effects on seed germination. Greenhouse pot experiments with sterile and non-sterile soil showed that consortia increased the total dry biomass of oat plants as compared to single strain inoculation and uninoculated controls. However, the positive impact on plant growth was less prominent when the bioinoculated strains had to compete with native soil microbes. Finally, the field experiment demonstrated that the consortium of vegetative cells was more efficient in promoting oat growth than the endospore consortium and the uninoculated control. Moreover, both consortia successfully colonized the roots and the rhizosphere of oat plants, without modifying the overall structure of the autochthonous soil microbial communities.

Use of Bacteria To Stabilize Archaeological Iron.

Iron artifacts are common among the findings of archaeological excavations. The corrosion layer formed on these objects requires stabilization after their recovery, without which the destruction of the item due to physicochemical damage is likely. Current technologies for stabilizing the corrosion layer are lengthy and generate hazardous waste products. Therefore, there is a pressing need for an alternative method for stabilizing the corrosion layer on iron objects. The aim of this study was to evaluate an alternative conservation-restoration method using bacteria. For this, anaerobic iron reduction leading to the formation of stable iron minerals in the presence of chlorine was investigated for two strains of Desulfitobacterium hafniense (strains TCE1 and LBE). Iron reduction was observed for soluble Fe(III) phases as well as for akaganeite, the most troublesome iron compound in the corrosion layer of archaeological iron objects. In terms of biogenic mineral production, differential efficiencies were observed in assays performed on corroded iron coupons. Strain TCE1 produced a homogeneous layer of vivianite covering 80% of the corroded surface, while on the coupons treated with strain LBE, only 10% of the surface was covered by the same mineral. Finally, an attempt to reduce iron on archaeological objects was performed with strain TCE1, which led to the formation of both biogenic vivianite and magnetite on the surface of the artifacts. These results demonstrate the potential of this biological treatment for stabilizing archaeological iron as a promising alternative to traditional conservation-restoration methods.IMPORTANCE Since the Iron Age, iron has been a fundamental material for the building of objects used in everyday life. However, due to its reactivity, iron can be easily corroded, and the physical stability of the object built is at risk. This is particularly true for archaeological objects on which a potentially unstable corrosion layer is formed during the time the object is buried. After excavation, changes in environmental conditions (e.g., higher oxygen concentration or lower humidity) alter the stability of the corrosion layer and can lead to the total destruction of the object. In this study, we demonstrate the feasibility of an innovative treatment based on bacterial iron reduction and biogenic mineral formation to stabilize the corrosion layer and protect these objects.

Nonchemical-vapor-deposition process for fabrication of highly efficient Yb-doped large core fibers.

A new fabrication process of active optical silica glass based on direct sand vitrification is proposed. This method, an alternative to chemical vapor deposition (CVD), allows the fabrication of homogeneous and highly Yb(3+)-doped rods that are ten times larger in diameter than those produced by CVD. For large-mode-area fibers fabricated by the stack-and-draw method, this is a tremendous technical breakthrough that could offer great flexibility in fiber design. As a proof of concept, we focused here on the fabrication and characterization of active core material surrounded by pure silica. Consequently, we draw a simple multimode step-index fiber. The index ripple in the core that matches our objectives is approximately 2.2x10(-4). For this first demonstration, the core material is codoped with Yb(2)O(3) (3600 parts in 10(6)(ppm) by weight) and Al(2)O(3), yielding a 180 dB m(-1) absorption at a wavelength of 975 nm, whereas the background loss is around 0.8 dB m(-1). The continuous-wave laser obtained with this fiber exhibits 74% slope efficiency.

Superbroadband fluorescence fiber fabricated with granulated oxides.

We demonstrate a single-core multiply doped fiber that, when pumped with a single pump source of approximately 800 nm, emits a more than two-octaves-spanning fluorescence spectrum ranging from 365 to 2300 nm. The fiber preform is manufactured from granulated oxides, and the core is doped with five different rare earths. At a pump power of 250 mW the total emitted power is 34 microW; given a core diameter of 6.5 microm and a numerical aperture of 0.1, the radiance exceeds 3 kW sr(-1) cm(-2). We also demonstrate direct diode pumping of the fiber.

Broadband emission from a multicore fiber fabricated with granulated oxides.

We demonstrate a multicore multidopant fiber which, when pumped with a single pump source around approximately 800 nm, emits a more than one octave-spanning fluorescence spectrum ranging from 925 to 2300 nm. The fiber preform is manufactured from granulated oxides and the individual cores are doped with five different rare earths, i.e., Nd3+, Yb3+, Er3+, Ho3+, and Tm3+.