Arbuscular mycorrhizal community structure on co-existing tropical legume trees in French Guiana

Aims We aimed to characterise the arbuscular mycorrhizal fungal (AMF) community structure and potential edaphic determinants in the dominating, but poorly described, root-colonizing Paris-type AMF community on co-occurring Amazonian leguminous trees. Methods Three highly productive leguminous trees (Dicorynia guianensis, Eperua falcata and Tachigali melinonii were targeted) in species-rich forests on contrasting soil types at the Nouragues Research Station in central French Guiana. Abundant AMF SSU rRNA amplicons (NS31-AM1 & AML1-AML2 primers) from roots identified via trnL profiling were subjected to denaturing gradient gel electrophoresis (DGGE), clone library sequencing and phylogenetic analysis. Results Classical approaches targeting abundant SSU amplicons highlighted a diverse root-colonizing symbiotic AMF community dominated by members of the Glomeraceae. DGGE profiling indicated that, of the edaphic factors investigated, soil nitrogen was most important in influencing the AMF community and this was more important than any host tree species effect. Conclusions Dominating Paris-type mycorrhizal leguminous trees in Amazonian soils host diverse and novel taxa within the Glomeraceae that appear under edaphic selection in the investigated tropical forests. Linking symbiotic diversity of identified AMF taxa to ecological processes is the next challenge ahead

First observations on the root morphology and symbioses of 21 major tree species in the primary tropical rain forest of French Guyana

A wide diversity of root morphology and symbiotic associations have been catalogued in 21 tree species in the tropical rain forest of French Guyana. Some unusual structures are described, such as nodular short roots containing hyphal coils. Endomycorrhizal symbiosis prevails in this type of forest. Parasitic nematodes (Meloidogyne sp) on young seedling roots of Dicorynia guianensis and Peltogyne venosa probably interfere with their regeneration.Premières observations sur la morphologie des racines et les symbioses racinaires de 21 espèces principales d'arbres en forêt tropicale humide primaire de Guyane française. Dans la forêt tropicale humide de Guyane française, une grande diversité de morphologie racinaire et d'associations symbiotiques a été observée sur 21 espèces d'arbres. Certaines structures inhabituelles sont décrites, comme des racines courtes noduleuses contenant des hyphes en pelotons. Les endomycorhizes constituent l'association symbiotique dominante dans ce type de forêt. Des galles à nématodes (Meloidogyne sp) fréquentes sur les racines des semis de Dicorynia guianensis et de Peltogyne venosa jouent probablement un rôle dans la régénération de ces espèces

Effect of endomycorrhizas and nematodes on the growth of seedlings of Dicorynia guianensis Amshoff, a tree species of the tropical rain forest in French Guiana

Seedlings of Dicorynia guianensis Amshoff, an economically important timber tree species of the primary tropical rain forest of French Guiana, were grown in pots containing a disinfected soil inoculated or not with forest soil, mycorrhizal roots of D guianensis or nematodes. Plant growth parameters and root endomycorrhizal colonization were measured after 200 days. The results are inconclusive about the role of nematodes but clearly show that D guianensis is dependent on endomycorrhizal symbiosis for its development: the top dry weights of the seedlings inoculated with soil or roots (with 87-84% endomycorrhizal roots) are 77 and 54% higher, respectively, than that of the uninoculated seedlings (with no mycorrhizas observed). In relation with previous observations in the forest, these results support the hypothesis that endomycorrhizas play a major role in the regeneration of D guianensis.Effet des endomycorhizes et des nématodes sur la croissance des semis de Dicorynia guianensis Amshoff, une essence de la forêt tropicale humide primaire de Guyane française. Des semis de D guianensis ont été cultivés en pots sur un sol désinfecté inoculé ou non avec un sol forestier, des racines mycorhizées de D guianensis ou des nématodes. Des paramètres de croissance des plantes et la colonisation endomycorhizienne des racines ont été mesurés au bout de 200 j. Les résultats ne sont pas concluants en ce qui concerne le rôle des nématodes, mais montrent clairement que D guianensis est dépendant de la symbiose endomycorhizienne pour son développement : les poids de matière sèche des parties aériennes des semis inoculés avec sol ou racines (aux racines endomy corhizées à 87-84 %) sont respectivement 77 et 54 % supérieurs à celui des semis témoins non inoculés (non mycorhizés). En relation avec des observations antérieures en forêt, ces résultats confortent l'hypothèse que les endomycorhizes jouent un rôle important dans la régénération de D guianensis

Continuous subcutaneous apomorphine infusion for the management of Parkinson's disease at the end-of-life

International audienceMeeting Abstract PM1-04