Symbiotic mycorrhizal fungi strongly influence plant establishment and growth, especially in stressful environments. Due to functional specificity of plant-mycorrhizal associations, inoculation with sympatric mycorrhizal symbionts has been proposed to enhance the performance of plants in restoration programs. However, the establishment and persistence of the plants' sympatric mycorrhizal communities in allopatric soil-climatic conditions is rarely addressed, and the potential of inoculations to support the restoration of plant cover and soil biota remains therefore largely unexplored. A field transplant experiment with Bouteloua gracilis spanning across four climatically defined sites in Northern Arizona has been utilized to determine the relative effects of initial inoculation, soil and site conditions on the composition of arbuscular mycorrhizal fungal communities in plant roots three seasons after their establishment. At each of the four sites, two B. gracilis genotypes were out-planted after pre-inoculation with either their "home" communities of microorganisms (originating from the site of seed collection of each genotype) or with the site-specific microbial community. Each inoculation treatment was created either in the "home" or in the site-specific soil. The root colonizing communities of arbuscular mycorrhizal fungi (AMF) were described by Illumina sequencing.
Results/Conclusions
The transfer of the "home" AMF communities in their "home" soils to the new sites did not significantly affect their composition, meaning that the site-specific climatic conditions and propagule input from surrounding vegetation were not important as factors. Across all four sites, the experimental factors: Inoculum, Site and Soil significantly affected the AMF community composition (PERMANOVA, P=0.001, adjR2=0.204/0.036/0.029, respectively). Altogether, they explained 28% of the variation in the AMF communities, the highest pure contribution being by Inoculum (8%). The effect of soil, relatively to the effect of initial inoculum, varied consistently between the four sites in the two plant genotypes. At two sites, the explained variation in community composition (ranging between 7% and 33% depending on site and plant genotype) was exclusively by initial inoculation, with no significant contribution of soil. The highest effect of inoculum was recorded for the combination of a more diverse "home" inoculum and "away" sites of low AMF diversity. The results suggest that inoculations with complex soil microbial inocula may contribute to the restoration of AMF communities in degraded ecosystems, but also points to the risks of geographical transfers of soil-plant material.