Floor vegetation management affects the diversity and composition of mycorrhizal symbionts and soil microbial communities in a Mediterranean olive orchard

Cover crops and natural grass cover, utilised for inter-row olive orchard floor management, protect soil from erosion, maintain organic matter and positively affect crop yield. Likewise, they increase soil microbial abundance, activity and diversity. This study assessed, across two years, the impact of cover crops preceded by deep tillage and undisturbed natural grass cover, on the diversity and composition of mycorrhizal symbionts and soil microbial communities, in a Mediterranean olive orchard. The natural grass cover consisted of a no-till treatment, with diversified natural vegetation. Soil samples were analysed using two molecular tools, Illumina Miseq sequencing and PCR-denaturing gradient gel electrophoresis (PCR-DGGE), to characterize soil microbial communities. Illumina Miseq sequencing identified 31 arbuscular mycorrhizal fungal (AMF) taxa, mainly belonging to the Glomeraceae family (84%), while the other taxa belonged to the Paraglomeraceae, Diversisporaceae and Ambisporaceae families. The use of cover crops preceded by deep tillage negatively affected AMF community composition during the first crop season, as compared with undisturbed natural grass cover. In the second year, when the deep tillage was not practiced, AMF Richness increased and a higher number of positive connections were established among the AMF community, as detected by co-occurrence network analysis. The cover crop treatment significantly increased bacterial diversity, leaving unchanged the fungal soil microbiota. Our findings suggest that, in order to maintain soil microbial abundance, activity and diversity, cover crops preceded by tillage may be used in inter-row olive orchard floor management as an alternative sustainable strategy, since AMF communities were able to re-establish in the short term and bacteria were positively affected.