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Summary: It is well understood that agricultural management influences arbuscular mycorrhizal (AM) fungi, but there is controversy about whether farmers should manage for AM symbiosis.We assessed AM fungal communities colonizing wheat roots for three consecutive years in a long‐term (> 14 yr) tillage and fertilization experiment. Relationships among mycorrhizas, crop performance, and soil ecosystem functions were quantified.Tillage, fertilizers and continuous monoculture all reduced AM fungal richness and shifted community composition toward dominance of a few ruderal taxa. Rhizophagus and Dominikia were depressed by tillage and/or fertilization, and their abundances as well as AM fungal richness correlated positively with soil aggregate stability and nutrient cycling functions across all or no‐tilled samples. In the field, wheat yield was unrelated to AM fungal abundance and correlated negatively with AM fungal richness. In a complementary glasshouse study, wheat biomass was enhanced by soil inoculum from unfertilized, no‐till plots while neutral to depressed growth was observed in wheat inoculated with soils from fertilized and conventionally tilled plots.This study demonstrates contrasting impacts of low‐input and conventional agricultural practices on AM symbiosis and highlights the importance of considering both crop yield and soil ecosystem functions when managing mycorrhizas for more sustainable agroecosystems. [ABSTRACT FROM AUTHOR]

The arbuscular mycorrhizal (AM) fungi are ubiquitous biotrophic root endophytes that form a significant link in macronutrient cycles. The AM fungi occupy two niches simultaneously, the intraradical niche, from which they gain carbon, and the bulk soil. We predict that AM community structure will vary through time, depending upon season and plant identity. In this study, we compared the AM fungal community colonising eight species of Acer L. (maple) grown in an arboretum. DNA from root samples was analysed using terminal restriction fragment length polymorphism (TRFLP) of AM fungal sequences. Three time points were sampled during the growing season, and ordination analysis showed this was the most important factor discriminating the TRFLP profiles. Analysis of each month separately showed that the host species was a significant factor in all samplings, but that the response of each species through time was different. This study demonstrates the dynamic nature of AM communities, and the importance of sampling habitats throughout the season to generate a complete picture of the AM community. Key words: maple, TRFLP, arbuscular mycorrhizas, communities, seasonality. Les champignons mycorhiziens a arbuscules (MA) sont des endophytes biotrophes ubiquistes des racines qui forment un lien significatif dans les cycles des macronutriments. Les champignons MA occupent simultanement deux niches, la niche intra-radicalaire, a partir de laquelle ils acquierent le carbone, et le sol en vrac. Nous predisons que la structure de la communaute de MA variera en fonction du temps, dependamment de la saison et de l'identite de la plante. Dans cette etude, nous comparons la communaute de champignons MA colonisant huit especes d'erables (Acer L.) cultives en arboretum. L'ADN d'echantillons de racines a ete analyse par polymorphisme de longueur de fragments de restriction terminaux (TRFLP) des sequences de MA fongiques. Trois periodes de temps ont ete echantillonnees durant la saison de croissance, et une analyse d'ordination a montre que cela constituait le facteur le plus important permettant de discriminer les profils en TRFLP. Une analyse de chacun des mois a montre separement que l'espece d'hote constituait un facteur significatif dans tous les echantillonnages, mais que la reponse de chaque espece etait differente en fonction du temps. Cette etude demontre la nature dynamique des communautes de MA et l'importance des habitats d'echantillonnage au cours de la saison, afin de dresser une image complete de la communaute de MA. [Traduit par la Redaction] Mots-cles: erable, TRFLP, mycorhize a arbuscules, communautes, saisonnalite., Introduction The arbuscular mycorrhizal (AM) symbiosis is the most widespread and abundant of all terrestrial mutualistic interactions. The symbiosis is thought to be generalist, in that those fungal taxa that [...]