Mycorrhizal fungi in Acacia mearnsii plantations and native fragments of the Pampas biome, southern Brazil

Black wattle (Acacia mearnsii) was introduced to southern Brazil in the 1930s without any documented history of microbial inoculation. This study tested the hypothesis that black wattle introduction does not harm indigenous arbuscular mycorrhizal fungi (AMF) communities or reduce soil AMF inoculum potential, probably because the species readily associates with a diverse range of native AMF. Soil samples were collected from areas with different land uses (native forest fragments, native pasture and black wattle plantations) and used in two greenhouse experiments. Experiment 1 assessed the inoculum potential of soils from different land uses by evaluating AMF root colonisation in Brachiaria (Urochloa brizantha) seedlings. Experiment 2 used Brachiaria and black wattle seedlings as trap plants to assess AMF spore diversity in the soil samples. AMF species were identified based on spore morphotypes. Results indicated that black wattle plantations did not significantly alter soil inoculum potential or AMF spore diversity, except in cases where soil P content was substantially affected by the plantation. Black wattle readily formed symbioses with diverse AMF communities upon introduction to a new environment. The most frequently observed AMF morphotypes in the black wattle rhizosphere were Claroideoglomus etunicatum and Rhizoglomus clarum, followed by Archaeospora trappei, Acaulospora colombiana, Acaulospora mellea, and two unidentified Glomus species. These findings align with the observation that black wattle has successfully adapted to the AMF diversity of southern Brazilian ecosystems.