Do soil microbes drive Acacia species invasion in non-native ranges in Australia?

Australian acacias are one of the most notable invaders worldwide. Across Australian states, acacias became invasive or even naturalized after being introduced to ecosystems outside their natural distribution range. The relative importance of soil biota in their invasion success remains unknown, particularly that of rhizobial and fungal communities. We tested the Enemy Release Hypothesis and the Acquired Mutualism Hypothesis to disentangle the belowground invasion mechanisms that may have assisted in the invasion success of these acacias across Australia

Plant-soil feedbacks do not explain invasion success of Acacia species in introduced range populations in Australia

Legumes, especially acacias, are considered amongst the most successful invaders globally. However there is still very little known about the role of soil microbial communities in their invasion success in novel ranges. We examined the role of the soil microbial community in the invasion success of four Acacia species (A. cyclops, A. longifolia, A. melanoxylon and A. saligna) and a close relative Paraserianthes lophantha, introduced into novel regions within Australia using a "black-box" approach. Seed and soil material were collected from multiple populations within each species' native and introduced range within Australia and used in a plant-soil feedback experiment to assess the effect of the soil microbial community on plant growth and nodulation. We found no effect, either positive or negative, of soil origin on species' performance, however there was a significant interaction between species and seed origin. Seed origin had a significant effect on the biomass of two species, A. cyclops and A. saligna. A. cyclops plants from the native range performed better across all soils than plants from the introduced range. The opposite trend was observed for A. saligna, with plants from the introduced range performing better overall than plants from the native range. Seed or soil origin did not have a significant effect on the presence and number of nodules suggesting that rhizobia do not constrain the invasion success of these legumes. Our results suggest that plant-soil feedbacks are unlikely to have played a significant role in the invasion success of these five species introduced into novel regions within Australia. This may be due to the widespread occurrence of acacias and their associated soil microbial communities throughout the Australian continent

A case study from Australia on five acacias and their associated soil microbial communities across non-native and native range populations

Although Australian acacias are one of the most notable invaders world-wide, relatively little is known about the role of soil microbial communities in their invasion success both globally and locally. In Australia, acacias have also become invasive or naturalized when introduced into novel locations across states. However, the relative importance of soil biota, particularly beneficial rhizobial and fungal communities, in the invasion success, remains unknown. We comprehensively examined the role of soil biota on the invasion success of four Acacia spp. (A. cyclops, A. longifolia, A. melanoxylon and A. saligna) and a close relative Paraserianthes lophantha in Australia. Soil and seed samples were collected from respective five native and non-native range populations of each species across four states (i.e. New South Wales, Victoria, South Australia and Western Australia). To assess the role of soil biota on plant performance we used (i) plant-soil feedback experiment to assess the net effect of soil microbiota on plant performance and (ii) 454 sequencing to identify the bacterial and fungal communities in the nodules and soils. Although some variation in microbial composition across the non-native and native populations was found, this did not translate into improved growth in the non-native range suggesting that other abiotic and biotic components (e.g. human imposed artificial selection, herbivory) may contribute more strongly to the invasion success of these acacias in non-native populations in Australia. Interestingly, we found that seed origin had stronger effect on plant performance than soil biota