The impact of tillage practices on arbuscular mycorrhizal fungal diversity in subtropical crops.

Arbuscular mycorrhizal fungi (AMF) are a main component of soil microbiota in most agrosystems. As obligately mutualistic symbionts, they colonize the roots of the majority of plants, including crop plants. We used molecular techniques to investigate how different tillage systems (moldboard, shred-bedding, subsoil-bedding, and no tillage) can influence the AM fungal community colonizing maize, bean, and sorghum roots in an experimental site located in northern Tamaulipas, Mexico. Roots from 36 plants were analyzed using AM fungal-specific primers to partially amplify the small subunit (SSU) of the ribosomal DNA genes. More than 880 clones were screened for restriction fragment length polymorphism (RFLP) variation, and 173 of these were sequenced. Ten AM fungal types were identified and clustered into three AM fungal families: Gigasporaceae, Glomaceae, and Paraglomaceae. Glomus was the dominating taxon in all the samples. Four of the 10 identified types were distinct from any previously published sequences and could correspond to either known unsequenced species or unknown species. The fungal diversity was low in the four agriculture management systems, but the multidimensional scaling (MDS) analysis and log-linear-saturated model indicated that the composition of the AMF community was significantly affected by the tillage system. In conclusion, since some fungal types were treatment specific, agricultural practices could directly or indirectly influence AM biodiversity.