Interconnectedness, length and viability of arbuscular mycorrhizal mycelium as affected by selected herbicides and fungicides

Arbuscular mycorrhizal fungi (AMF) play a key role in plant nutrition and in the maintenance of soil fertility in agroecosystems, but their survival can be affected by different agricultural practices, including the use of pesticides. In this work, we assessed the impact of chemicals with herbicidal and fungicidal activity on mycelial growth and structure of the worldwide distributed AMF Funneliformis mosseae. Results showed that mycelial growth and interconnectedness of three different F. mosseae lineages were affected by the chemicals tested at concentrations lower than those indicated for agricultural use. Indeed, benomyl reduced mycelial growth in one lineage and fenhexamid negatively affected germlings growth in the three lineages, while both fungicides significantly affected mycelial viability and induced abnormal hyphal branching. The three F. mosseae lineages showed sensitivity to herbicides, with significant growth and viability decreases in the presence of the active ingredient glufosinate ammonium and a low viability at increasing concentrations of dicamba. Anastomosis rates were reduced by the two fungicides and by very low levels of the herbicide glufosinate, whose impact on AMF networks should be further investigated, given its wide use in agriculture. Our results suggest that the use of some pesticides in agroecosystems may lead to growth reduction and disruption of AMF mycelial structural traits, even in AMF species able to tolerate soil disturbance, posing serious threats to AMF symbiotic performance and to the maintenance of soil mycorrhizal potential.