The effect of ecological restoration on mutualistic services provided by arbuscular mycorrhizal fungi depends on site location and host identity

Arbuscular mycorrhizal (AM) fungi form soil hyphal networks that facilitate plant nutrient uptake. AM fungi can be less effective plant-mutualists in cultivated fields because agricultural stressors reduce their functional diversity and may favour a less mutualistic genotype. Previously, we showed restoration of retired cultivated fields stimulated AM fungal species diversity. Here, we tested if restoration also stimulated mutualistic functions of AM fungi.

Soil inoculum was collected from five farm sites in cultivated fields and adjacent prairies that had been restored 8–12 years previously. Plant-growth promoting functions of AM fungi were quantified under greenhouse conditions by comparing biomass and phosphorus content in Trifolium pratense and Andropogon gerardii plants whose access to AM fungal networks was severed or left intact.

Plant biomass was higher in the intact vs. severed AM fungal network treatment but the mean effect did not differ between restored prairie and cultivated field inoculum. Nonetheless, soil inoculum source effect on biomass depended on site location for T. pratense, but not A. gerardii. Access to AM fungal networks from cultivated fields increased phosphorus in T. pratense, but reduced phosphorus in A. gerardii, compared to restored prairies. Soil inoculum source effects on phosphorus also depended on farm site location.

Ecological restoration did not universally increase mutualistic functions of AM fungi. However, the fact that plant responses to AM fungi were dependent on site location and host identity suggests that ecological restoration has complex effects on the mutualistic benefits that plants receive from AM fungi.