Search

Reciprocal effects between arbuscular mycorrhizal fungi (AMF) and plant communities are essential to study the complexity of interactions in a grassland ecosystem. Here, we investigated the effects of plant community density and composition on AMF colonization, plant growth, and reproduction investment. We developed an experimental system with three compartments, each containing either three or sixMedicago truncatula Gaertn. plants, or three M. truncatula plants associated with three Silene vulgaris (Moench) Garcke plants. All three compartments shared the same common mycorrhizal network built either by Rhizophagus irregularis MUCL 43194, by Rhizophagus clarus MUCL 46238, or by both AMF in association grown in a central compartment on Plantago lanceolata L. Our results demonstrate an absence of effect of plant density but a positive influence of mixed cultures on AMF root colonization compared with monocultures. This higher AMF development resulted in a positive feedback on shoot biomass and number of flowers and fruits produced by M. truncatula. Although both fungal strains were present in root systems, co-inoculation did not generate a synergistic effect on plant development. These results highlight the importance of plant associations on AMF dynamics, which requires further investigation at the community scale to improve our understanding of the intricate AMF--host plant relationships. Key words: common mycorrhizal network, arbuscular mycorrhizal fungi, Medicago-Silene mixed cultures, root colonization, plant reproduction investment. Les effets reciproques entre les champignons mycorhiziens arbusculaires (CMA) et les communautes vegetales sont essentiels pour etudier la complexite des interactions dans un ecosysteme de prairie. Les auteurs ont examine ici les effets de la densite et de la composition d'une communaute vegetale sur la colonisation par les CMA, la croissance vegetale et l'investissement reproductif. Ils ont developpe un systeme experimental comportant trois compartiments, chacun contenant trois ou six plants de Medicago truncatula Gaertn., ou trois plants de M. truncatula associes a trois plants de Silene vulgaris (Moench) Garcke. Les trois compartiments partageaient le meme reseau mycorhizien construit soit par Rhizophagus irregularis MUCL 43194, par Rhizophagus clarus MUCL 46238 ou par les deux CMA cultives en association dans un compartiment central sur Plantago lanceolata L. Leurs resultats demontrent une absence d'effet de la densite des vegetaux mais une influence positive des cultures melangees sur la colonisation racinaire par les CMA comparativement aux monocultures. Ce developpement de CMA plus eleve a resulte en une retroaction positive sur la biomasse de pousses et le nombre de fleurs et de fruits produits par M. truncatula. Meme si les deux souches fongiques etaient presentes dans les systemes racinaires, la co-inoculation ne generait pas d'effet synergique sur le developpement des vegetaux. Ces resultats soulignent l'importance des associations vegetales sur la dynamique des CMA, laquelle requiert d'etre examinee plus en profondeur a l'echelle de la communaute afin d'ameliorer la comprehension des relations complexes CMA--plantes hotes. [Traduit par la Redaction] Mots-cles : reseau mycorhizien commun, champignons mycorhiziens arbusculaires, cultures melangees Medicago-Silene, colonisation racinaire, investissement reproductif des vegetaux., Introduction Arbuscular mycorrhizal fungi (AMF) establish symbiosis with the roots of over two-thirds of plant species; they are likely the most abundant mutualistic association in terrestrial ecosystems (Parniske 2008). These [...]

Arbuscular mycorrhizal fungi ( AMF) are key determinants of plant interactions in ecosystems. Through their effects on competition, they are regulators of the structure of communities. Conversely, the composition of plant assemblages may also influence the AMF colonization dynamics of plant species. Here, we tested under in vitro culture conditions the effects of M edicago truncatula, a highly mycorrhizal plant species, and S ilene vulgaris, a weakly mycorrhizal plant species, grown single (monospecies treatments) or in combination (bispecies treatment) on the colonization dynamics of the AMF R hizophagus irregularis MUCL 43194. The seedlings were placed in a pre-established hyphal network developing from a mature M . truncatula mycorrhizal donor plant. Extraradical mycelium ( ERM) and root colonization parameters as well as root morphology were measured over a period of 12 days. An increased ERM length, total root colonization and proportion of arbuscules were noted in the bispecies treatment. Conversely, the bispecies treatment seemed to have no effect on root growth. This study also demonstrated the suitability of the in vitro culture system for studying the interactions between AMF and host plants grown as mono- and bispecies combinations. [ABSTRACT FROM AUTHOR]

The ubiquitous arbuscular mycorrhizal fungi consume significant amounts of plant assimilated C, but this C flow has been difficult to quantify. The neutral lipid fatty acid 16:1ω5 is a quantitative signature for most arbuscular mycorrhizal fungi in roots and soil. We measured carbon transfer from four plant species to the arbuscular mycorrhizal fungus Glomus intraradices by estimating 13C enrichment of 16:1ω5 and compared it with 13C enrichment of total root and mycelial C. Carbon allocation to mycelia was detected within 1 day in monoxenic arbuscular mycorrhizal root cultures labeled with [13C] glucose. The 13C enrichment of neutral lipid fatty acid 16:1ω5 extracted from roots increased from 0.14% 1 day after labeling to 2.2% 7 days after labeling. The colonized roots usually were more enriched for 13C in the arbuscular mycorrhizal fungal neutral lipid fatty acid 16:1ω5 than for the root specific neutral lipid fatty acid 18:2ω6,9. We labeled plant assimilates by using 13CO2 in whole-plant experiments. The extraradical mycelium often was more enriched for 13C than was the intraradical mycelium, suggesting rapid translocation of carbon to and more active growth by the extraradical mycelium. Since there was a good correlation between 13C enrichment in neutral lipid fatty acid 16:1ω5 and total 13C in extraradical mycelia in different systems (r2 = 0.94), we propose that the total amount of labeled C in intraradical and extraradical mycelium can be calculated from the 13C enrichment of 16:1ω5. The method described enables evaluation of C flow from plants to arbuscular mycorrhizal fungi to be made without extraction, purification and identification of fungal mycelia. [ABSTRACT FROM AUTHOR]

The ubiquitous arbuscular mycorrhizal fungi consume significant amounts of plant assimilated C, but this C flow has been difficult to quantify. The neutral lipid fatty acid 16:1omega5 is a quantitative signature for most arbuscular mycorrhizal fungi in roots and soil. We measured carbon transfer from four plant species to the arbuscular mycorrhizal fungus Glomus intraradices by estimating (13)C enrichment of 16:1omega5 and compared it with (13)C enrichment of total root and mycelial C. Carbon allocation to mycelia was detected within 1 day in monoxenic arbuscular mycorrhizal root cultures labeled with [(13)C]glucose. The (13)C enrichment of neutral lipid fatty acid 16:1omega5 extracted from roots increased from 0.14% 1 day after labeling to 2.2% 7 days after labeling. The colonized roots usually were more enriched for (13)C in the arbuscular mycorrhizal fungal neutral lipid fatty acid 16:1omega5 than for the root specific neutral lipid fatty acid 18:2omega6,9. We labeled plant assimilates by using (13)CO(2) in whole-plant experiments. The extraradical mycelium often was more enriched for (13)C than was the intraradical mycelium, suggesting rapid translocation of carbon to and more active growth by the extraradical mycelium. Since there was a good correlation between (13)C enrichment in neutral lipid fatty acid 16:1omega5 and total (13)C in extraradical mycelia in different systems (r(2) = 0.94), we propose that the total amount of labeled C in intraradical and extraradical mycelium can be calculated from the (13)C enrichment of 16:1omega5. The method described enables evaluation of C flow from plants to arbuscular mycorrhizal fungi to be made without extraction, purification and identification of fungal mycelia.