Diversity and composition of mycorrhizal simbionts and soil microbial communities are affected by floor management in a Mediterranean olive orchard

Intensive and super-intensive olive cropping systems, combined with frequent tillage of orchard floors and the large use of chemical fertilizers and pesticides can heavily affect soil microbial communities. On the other hand, the use of cover crops and natural grass cover in olive orchards may provide several soil benefits and enhance the abundance, activity and diversity of soil microbiota. This work investigated the effects of cover crops, preceded by deep tillage, compared to undisturbed natural grass cover on the diversity and composition of arbuscular mycorrhizal fungi (AMF) and soil microbial communities in a Mediterranean olive orchard, over a two-year period. The natural grass cover treatment consisted of no-till management with diversified natural vegetation. For each treatment, three replicate composite soil samples were analysed using molecular approaches, Illumina MiSeq sequencing and PCR-denaturing gradient gel electrophoresis (PCR-DGGE). Molecular analyses identified 31 AMF taxa, predominantly from the Glomeraceae family (84%). Some AMF taxa demonstrated resilience to deep tillage, which was the main factor influencing AMF community composition during the first cropping season. The cover crop treatment significantly increased bacterial diversity, while fungal diversity remained stable. Our results indicate that cover crops preceded by tillage can be an effective and sustainable inter-row management strategy in olive orchards, supporting the short-term re-establishment of AMF communities and positively impacting bacterial diversity, thereby contributing to soil health and agroecosystem resilience.