Spectral Composition of Sunlight Affects the Microbial Functional Structure of Beech Leaf Litter During the Initial Phase of Decomposition

Aims This study tests whether different spectral regions of sunlight affect the microbial decomposer assemblage in surface leaf litter in a beech understorey over the first 6 months following leaf senescence. Methods We performed a litterbag experiment employing filters attenuating combinations of UV-B, UV-A, blue, and green light as well as the whole spectrum of sunlight. We measured changes in microbial biomass and community structure, litter mass loss and litter chemistry during the first 6 months of decomposition. Results Fungal and total microbial biomass were highest in the treatment excluding UV radiation, blue and green light. Exclusion of UV-B radiation decreased the fungal:bacterial biomass ratio and litter nitrogen content. Bacterial biomass was lower in the dark treatment compared to treatments receiving at least part of the solar spectrum. Our filter treatments affected microbial functional structure from the beginning of the experiment, whereas mass loss was only significantly affected after 6 months of decomposition and no effect was found on litter carbon content. Conclusions This study proves that sunlight, in a spectrally dependent manner, affects both microbial functional structure and biomass in temperate deciduous forests early in the decomposition process, with bacteria tending to dominate in sunlight and fungi in dark conditions. We found sunlight to be important in the decomposition in temperate forest understoreys despite the low irradiance characterizing these environments. However, long-term studies are required to estimate the relative contribution of sunlight among factors affecting the eventual incorporation of decomposing leaf litter into forest soils.Peer reviewe

Les agents de la bioremédiation des sols pollués par les hydrocarbures polycycliques aromatiques

International audienceSoil PAHs contamination is now becoming of great concern. This pollution has a negative impact on activities directly or indirectly related to the soil, but it has also potential consequences for human health and the quality of the ecosystem. Indeed, polycyclic aromatic hydrocarbons (PAHs) represent an important class of environmental pollutants, of which some are known to be mutagenic and carcinogenic. Consequently, the US Environmental Protection Agency (EPA) has listed some PAHs among the priority pollutants to be monitored in aquatic and terrestrial ecosystems. Bioremediation, the use of organisms for the treatment of soil pollution, have received considerable interest in recent years because of its ecological aspect and because of potential cost savings compared to conventional non biological techniques. The objective of this paper is to review findings concerning the potential of the organisms used for bioremediation of soils polluted with PAHs. At present, numerous organisms (bacteria, fungi, algae and plants) are reported to metabolise PAHs. The several enzymatic mechanisms known to be involved in the PAHs degradation by the different biological systems will be underlined.Parmi les techniques de dépollution et de réhabilitation des sols (physiques, chimiques et biologiques), la bioremédiation (détoxification ou minéralisation d'un polluant par les organismes vivants) des sols in situ semble être une méthode d'intérêt d'un point de vue économique et écologique. Contrairement aux autres procédés (incinération, lessivage du sol…) où les polluants sont souvent transférés et non détruits, la biodégradation peut permettre la minéralisation du xénobiotique, et donc sa disparition. De plus, cette technique est particulièrement adaptée pour le traitement des hydrocarbures polycycliques aromatiques (HPAs), contaminants comptant parmi les plus récalcitrants et les plus toxiques (pouvoirs cancérigène et mutagène). Il a été démontré que de nombreux organismes, procaryotes ou eucaryotes (algues, bactéries, champignons, plantes), possèdent la capacité à dégrader les HPAs. La présente revue a pour but de faire le point sur l'état actuel des connaissances concernant les organismes utilisés en tant qu'agents biologiques efficaces de dépollution des sols contaminés par les HPAs. Les systèmes enzymatiques impliqués dans la dégradation des HPAs chez ces différents systèmes biologiques seront décrits

Dioxins/furans disturb the life cycle of the arbuscular mycorrhizal fungus, Rhizophagus irregularis and chicory root elongation grown under axenic conditions

International audienceArbuscular mycorrhizal fungi (AMF)-assisted phytoremediation is a promising technology for sustainable removal of hazardous pollutants like dioxins/furans (PCDD/F) from the soil. However, little is known on AMF development in the presence of the persistent organic pollutants, PCDD/F. Thus, the present work aims at investigating the impact of increasing PCDD/F concentrations on the development of both partners of the symbiosis: the AMF, Rhizophagus irregularis and the chicory roots, Cichorium intybus L. grown under axenic conditions. Our results show that even R. irregularis spore germination is not affected by PCDD/F, it occurred mainly in linear way. However, root colonization, extra-radical hyphal elongation and sporulation are reduced by 40, 30, and 75%, respectively, at the highest PCDD/F concentration. In addition, while non-mycorrhizal root growth (length and dry weight) decreased at the highest PCDD/F concentration, no negative effect was observed on the dry weight of mycorrhizal roots. In conclusion, our findings show that although high PCDD/F concentrations disturb the main stages of R. irregularis development, the AMF remains able to fulfill its life cycle in the presence of PCDD/F. Moreover, the mycorrhizal inoculation protects the host plant against PCDD/F phytotoxicity. AMF could thus represent an interesting amendment option to assist phytoremediation of PCDD/F contaminated soils

Essential Oils as Potential Alternative Biocontrol Products against Plant Pathogens and Weeds: A Review

International audienceNaturally produced by aromatic plants, essential oils (EO) contain a wide range of volatile molecules, including mostly secondary metabolites, which possess several biological activities. Essential oils properties such as antioxidant, antimicrobial and anti-inflammatory activities are known for a long time and hence widely used in traditional medicines, cosmetics and food industries. However, despite their effects against many phytopathogenic fungi, oomycetes and bacteria as well as weeds, their use in agriculture remains surprisingly scarce. The purpose of the present review is to gather and discuss up-to-date biological activities of EO against weeds, plant pathogenic fungi, oomycetes and bacteria, reported in the scientific literature. Innovative methods, potentially valuable to improve the efficiency and reliability of EO, have been investigated. In particular, their use towards a more sustainable agriculture has been discussed, aiming at encouraging the use of alternative products to substitute synthetic pesticides to control weeds and plant diseases, without significantly affecting crop yields. An overview of the market and the recent advances on the regulation of these products as well as future challenges to promote their development and wider use in disease management programs is described. Because of several recent reviews on EO insecticidal properties, this topic is not covered in the present review

Significance of Arbuscular Mycorrhizal Fungi in Mitigating Abiotic Environmental Stress in Medicinal and Aromatic Plants: A Review

Medicinal and aromatic plants (MAPs) have been used worldwide for thousands of years and play a critical role in traditional medicines, cosmetics, and food industries. In recent years, the cultivation of MAPs has become of great interest worldwide due to the increased demand for natural products, in particular essential oils (EOs). Climate change has exacerbated the effects of abiotic stresses on the growth, productivity, and quality of MAPs. Hence, there is a need for eco-friendly agricultural strategies to enhance plant growth and productivity. Among the adaptive strategies used by MAPs to cope with the adverse effects of abiotic stresses including water stress, salinity, pollution, etc., their association with beneficial microorganisms such as arbuscular mycorrhizal fungi (AMF) can improve MAPs’ tolerance to these stresses. The current review (1) summarizes the effect of major abiotic stresses on MAPs’ growth and yield, and the composition of EOs distilled from MAP species; (2) reports the mechanisms through which AMF root colonization can trigger the response of MAPs to abiotic stresses at morphological, physiological, and molecular levels; (3) discusses the contribution and synergistic effects of AMF and other amendments (e.g., plant growth-promoting bacteria, organic or inorganic amendments) on MAPs’ growth and yield, and the composition of distilled EOs in stressed environments. In conclusion, several perspectives are suggested to promote future investigations

Développement d’une filière éco-innovante de valorisation non alimentaire de phytomasse produite sur des sols contaminés par des éléments traces métalliques : production d’huiles essentielles

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Into the wild blueberry ( Vaccinium angustifolium ) rhizosphere microbiota

International audienceThe ability of wild blueberries to adapt to their harsh environment is believed to be closely related to their symbiosis with ericoid mycorrhizal fungi, which produce enzymes capable of organic matter mineralization. Although some of these fungi have been identified and characterized, we still know little about the microbial ecology of wild blueberry. Our study aims to characterize the fungal and bacterial rhizosphere communities of Vaccinium angustifolium (the main species encountered in wild blueberry fields). Our results clearly show that the fungal order Helotiales was the most abundant taxon associated with V. angustifolium. Helotiales contains most of the known ericoid mycorrhizal fungi which are expected to dominate in such a biotope. Furthermore, we found the dominant bacterial order was the nitrogen-fixing Rhizobiales. The Bradyrhizobium genus, whose members are known to form nodules with legumes, was among the 10 most abundant genera in the bacterial communities. In addition, Bradyrhizobium and Roseiarcus sequences significantly correlated with higher leaf-nitrogen content. Overall, our data documented fungal and bacterial community structure differences in three wild blueberry production fields

Etude des performances de phytoextraction du Zn et du Cd de l'hyperaccumulateur Arabidopsis halleri en co-culture avec le Saule

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Phytoextraction in situ du Zn et du Cd de l’hyperaccumulateur Arabidopsis halleri en co-culture avec le saule des vanniers

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