Mycorrhizal Communities associated with Soil Aggregates in the Rhizosphere of Willows (Salix Spp.) Inoculated with Rhizophagus intraradices and Hebeloma cylindrosporum inoculants

Mycorrhizae improve plant growth and ecosystem sustainability by forming a symbiotic association with higher plants including the economically important willows (Salix spp.). With the recognition of the importance of mycorrhizae in terrestrial ecosystems, inoculation of plants with mycorrhizae is becoming a common practice in agricultural and land reclamation industries. However, little information is available on important ecological parameters such as soil aggregation, soil organic carbon content (SOC) and mycorrhizal communities associated with willow rhizospheres in response to mycorrhizal inoculation in willow systems. The main objectives of this research were to explore how commercial mycorrhizal inoculation of willows impacts (1) percent water-stable soil aggregates (%WSA); (2) indigenous arbuscular mycorrhizal fungi (AMF) and ectomycorrhizal fungi (EMF) community composition associated with different size soil aggregates; (3) SOC, and (4) willow growth. These objectives were examined under both greenhouse and field conditions. Using molecular approaches, we observed the existence of spatial variability in indigenous AMF communities among different soil aggregate size classes. This spatial variability varied with type of soil and could be reduced by inoculating with a commercial AMF inoculant. The indigenous EMF diversity was low and did not show spatial heterogeneity among soil aggregates, but it did vary with soil type. In addition, other parameters, including %WSA, SOC within the willow rhizosphere, and willow plant growth also varied by soil type and changed in association with commercial mycorrhizal inoculation. In the field experiment, soil extracts from willow nursery soil had comparable plant growth promotion with commercial mycorrhizal inoculation, and altered the AMF community associated with bulk soil and soil aggregates in the willow rhizosphere. These results suggest that historically superior willow growth in the willow nursery soil could be due to pre-existing soil microbiological factors. Overall this research indicates that AMF and EMF inoculation has the potential to influence the composition of the AMF community, but had little influence on the composition of the EMF community in the systems tested.