Interactions of Arbuscular Mycorrhizal Fungi with Rhizosphere Communities in Saline Soils

Soil salinity is a major constraint for crop production worldwide. Among many soil fertility issues associated with saline soils, phosphorus unavailability is most commonly noticed. Improving plant interactions with arbuscular mycorrhizal fungi (AMF) and other soil microbes have been widely shown to contribute to salinity tolerance and increase phosphorus (P) availability. However, there are many knowledge gaps to effectively improve AMF interactions in saline soils. Lower abundance of AMF is one of the limitations for increasing root colonization in saline soils. Supplementation of salt tolerant AMF spores is an emerging practice, however, identifying competent AMF species or combination of species beneficial at high salt concentration is a challenge. It is also not clear how introduced AMF species would interact with other native soil communities to influence phosphorus availability. Additionally, it is not clear whether improving soil conditions using a soil amendment can further enhance AMF interaction and colonization. In order to address these knowledge gaps, three experiments were conducted in a naturally saline soil to investigate: (1) the effects of AMF inoculation on plant growth and root colonization at different salinity levels, (2) the role of indigenous soil microbes with AMF inoculation to increase P availability to plants and (3) the combined effects of soil amendment and AMF inoculation on root colonization and P availability to plants. Microcosms were setup in growth chamber-based experiments to address above objectives separately. Results from the first experiment showed significantly different level of root colonization (p <0.05) among the three species of AMF inocula, and that colonization was generally higher with increasing salt concentrations, with some significant differences between the inoculum species. Plant growth responses were significantly different between the AMF species as well. These results suggest that artificial inoculation can increase root colonization in saline soils, although at different levels by AMF species at different salinity levels. In the second experiment, soil sterilization significantly (p <0.05) reduced soil extractable P, ALP activity, phoD and fungal ITS gene abundances in the hyphosphere soil in both AMF-inoculated and uninoculated treatments. However, AMF inoculation in unsterilized soils resulted in a significantly (p <0.05) higher plant P uptake compared to uninoculated in both sterilized and unsterilized soils. These results indicate that AMF-hyphosphere microbial community interactions play a synergistic role in increasing P availability in salt-affected soils. Findings of the third experiment indicated that combined application of BC and AMF significantly improved (p <0.05) plant shoot and root growth, plant P uptake, extractable P in bulk soil, and microbial community abundance in the rhizosphere compared to control. However, addition of BC significantly (p