Improving the growth of oak plantations using controlled mycorrhizrtion: Results from 12 experiments in north-erstern France

The growth of bare-root oak seedlings (Quercus petraea and Quercus robur), mycorrhized with Thelephora terrestris or four other fungi by means of nursery inoculation, was compared after outplanting in 12 clear-cut forest sites in North-Eastern France. Some strains of Paxillus involutus and Laccaria bicolor proved to be good candidates for routine inoculation in oak nurseries, compared to Thelephora terrestris, which is the dominant fungal symbiont, associated with commercial oak planting stock in France. They provide significant extra growth, resulting in reduced competition from the vegetation. However, the effect is nil if seedlings are planted in a grassy meadow.La croissance de semis de Chêne (Quercus petraea et Quercus robur) à racines nues, mycorhizés par Thelephora terrestris ou quatre autres champignons par inoculation en pépinière, a été comparée après plantation dans 12 parcelles forestières coupées à blanc dans le Nord-Est de la France. Certaines souches de Paxillus involutus et de Laccaria bicolor se sont révélées être de bonnes candidates pour l’inoculation en routine des pépinières de Chêne, par rapport à Thelephora terrestris qui est le principal symbionte fongique associé aux plants commerciaux de Chêne en France. Elles procurent un gain de croissance significatif, avec comme résultat une moindre compétition de la part de la végétation. Cependant, l’effet est nul si les semis sont plantés dans une prairie de graminées

Amélioration de la croissance des plantations de chêne par mycorhization contrôlée : bilan de 12 essais dans le Nord-est de la France

National audienceLa croissance de semis de Chêne (Quercus petraea et Quercus robur) à racines nues, mycorhizés par Thelephora terrestris ou quatre autres champignons par inoculation en pépinière, a été comparée après plantation dans 12 parcelles forestières coupées à blanc dans le Nord-Est de la France. Certaines souches de Paxillus involutus et de Laccaria bicolor se sont révélées être de bonnes candidates pour l’inoculation en routine des pépinières de Chêne, par rapport à Thelephora terrestris qui est le principal symbionte fongique associé aux plants commerciaux de Chêne en France. Elles procurent un gain de croissance significatif, avec comme résultat une moindre compétition de la part de la végétation. Cependant, l’effet est nul si les semis sont plantés dans une prairie de graminées

Effect of poplar genotypes on mycorrhizal infection and secreted enzyme activities in mycorrhizal and non-mycorrhizal roots

International audienceThe impact of ectomycorrhiza formation on the secretion of exoenzymes by the host plant and the symbiont is unknown. Thirty-eight F-1 individuals from an interspecific Populus deltoides (Bartr.)xPopulus trichocarpa (Torr. & A. Gray) controlled cross were inoculated with the ectomycorrhizal fungus Laccaria bicolor. The colonization of poplar roots by L. bicolor dramatically modified their ability to secrete enzymes involved in organic matter breakdown or organic phosphorus mobilization, such as N-acetylglucosaminidase, beta-glucuronidase, cellobiohydrolase, beta-glucosidase, beta-xylosidase, laccase, and acid phosphatase. The expression of genes coding for laccase, N-acetylglucosaminidase, and acid phosphatase was studied in mycorrhizal and non-mycorrhizal root tips. Depending on the genes, their expression was regulated upon symbiosis development. Moreover, it appears that poplar laccases or phosphatases contribute poorly to ectomycorrhiza metabolic activity. Enzymes secreted by poplar roots were added to or substituted by enzymes secreted by L. bicolor. The enzymatic activities expressed in mycorrhizal roots differed significantly between the two parents, while it did not differ in non-mycorrhizal roots. Significant differences were found between poplar genotypes for all enzymatic activities measured on ectomycorrhizas except for laccases activity. In contrast, no significant differences were found between poplar genotypes for enzymatic activities of non-mycorrhizal root tips except for acid phosphatase activity. The level of enzymes secreted by the ectomycorrhizal root tips is under the genetic control of the host. Moreover, poplar heterosis was expressed through the enzymatic activities of the fungal partner

A Transcriptomic Atlas of the Ectomycorrhizal Fungus Laccaria bicolor

Trees are able to colonize, establish and survive in a wide range of soils through associations with ectomycorrhizal (EcM) fungi. Proper functioning of EcM fungi implies the differentiation of structures within the fungal colony. A symbiotic structure is dedicated to nutrient exchange and the extramatricular mycelium explores soil for nutrients. Eventually, basidiocarps develop to assure last stages of sexual reproduction. The aim of this study is to understand how an EcM fungus uses its gene set to support functional differentiation and development of specialized morphological structures. We examined the transcriptomes of Laccaria bicolor under a series of experimental setups, including the growth with Populus tremula x alba at different developmental stages, basidiocarps and free-living mycelium, under various conditions of N, P and C supply. In particular, N supply induced global transcriptional changes, whereas responses to P supply seemed to be independent from it. Symbiosis development with poplar is characterized by transcriptional waves. Basidiocarp development shares transcriptional signatures with other basidiomycetes. Overlaps in transcriptional responses of L. bicolor hyphae to a host plant and N/C supply next to co-regulation of genes in basidiocarps and mature mycorrhiza were detected. Few genes are induced in a single condition only, but functional and morphological differentiation rather involves fine tuning of larger gene sets. Overall, this transcriptomic atlas builds a reference to study the function and stability of EcM symbiosis in distinct conditions using L. bicolor as a model and indicates both similarities and differences with other ectomycorrhizal fungi, allowing researchers to distinguish conserved processes such as basidiocarp development from nutrient homeostasis

Effet de la substitution d'essence sur le fonctionnement et la durabilité des écosystèmes forestiers : l'apport des travaux pluridisciplinaires menés en forêt de Breuil Chenue - Morvan

National audienceLe site-atelier de Breuil (Morvan), appartenant à l’Observatoire de Recherche sur l’Environnement F-ORE-T, est un support opérationnel des travaux actuels sur les cycles biogéochimiques en relation avec la diversité biologique du sol. De nombreux projets multidisciplinaires sont en cours sur ce site dont l’objectif commun est d’améliorer les connaissances sur les effets physiques, chimiques et biologiques des substitutions d’essences. Des travaux y sont menés à différentes échelles temporelles et spatiales, de l’instantané au pluriannuel, du microsystème fonctionnel jusqu’à l’écosystème complet. Les travaux développés à Breuil depuis 2001, montrent que les essences ont affecté les cycles clé du carbone et de l’azote avec les conséquences sur le fonctionnement des cycles de tous les autres éléments. Ces modifications sont entre autres liées à un contrôle des populations de micro-organismes du sol par les essences forestières qui les structurent. Les recherches en cours tentent d’élucider cette question pertinente d’écologie. Compte tenu de la longévité des essences forestières, ce site devra être suivi sur le long terme, vraisemblablement par une approche diachronique

Whole-body MR imaging in suspected physical child abuse: comparison with skeletal survey and bone scintigraphy findings from the PEDIMA prospective multicentre study

International audienceObjectives: To assess the contribution of whole-body magnetic resonance imaging (WBMRI) and bone scintigraphy (BS) in addition to skeletal survey (SS) in detecting traumatic bone lesions and soft-tissue injuries in suspected child abuse.Methods: In this prospective, multicentre, diagnostic accuracy study, children less than 3 years of age with suspected physical abuse were recruited. Each child underwent SS, BS and WBMRI. A blinded first review was performed in consensus by five paediatric radiologists and three nuclear medicine physicians. A second review investigated discrepancies reported between the modalities using a consensus result of all modalities as the reference standard. We calculated the sensitivity, specificity and corresponding 95% confidence interval for each imaging modality (SS, WBMRI and BS) and for the combinations [SS + WBMRI] and [SS + BS].Results: One hundred seventy children were included of which sixty-four had at least one lesion. In total, 146 lesions were included. The sensitivity and specificity of each examination were, respectively, as follows: 88.4% [95% CI, 82.0-93.1] and 99.7% [95% CI, 99.5-99.8] for the SS, 69.9% [95% CI, 61.7-77.2] and 99.5% [95% CI, 99.2-99.7] for WBMRI and 54.8% [95% CI, 46.4-63.0] and 99.7% [95% CI, 99.5-99.9] for BS. Sensitivity and specificity were, respectively, 95.9% [95% CI, 91.3-98.5] and 99.2% [95% CI, 98.9-99.4] for the combination SS + WBMRI and 95.2% [95% CI, 90.4-98.1] and 99.4% [95% CI, 99.2-99.6] for the combination SS + BS, with no statistically significant difference between them.Conclusion: SS was the most sensitive independent imaging modality; however, the additional combination of either WBMRI or BS examinations offered an increased accuracy.Key points: • SS in suspected infant abuse was the most sensitive independent imaging modality in this study, especially for detecting metaphyseal and rib lesions, and remains essential for evaluation. • The combination of either SS + BS or SS + WBMRI provides greater accuracy in diagnosing occult and equivocal bone injuries in the difficult setting of child abuse. • WBMRI is a free-radiation technique that allows additional diagnosis of soft-tissue and visceral injuries