Native grass cover as a field indicator of mycorrhizal inoculum potential in southwestern drylands

Abstract Introduction Drylands experience disturbances that can lead to shifts in plant and microbial communities. Arbuscular mycorrhizal (AM) fungi help mediate establishment, survival, and resource flow within above‐ and belowground communities and have the potential to be used as a restoration tool to facilitate revegetation under disturbance regimes. Objectives To better understand how AM fungal abundance changes with disturbance and examine its restoration potential, we sampled soils across a gradient of sites in the southwestern United States. We hypothesized that (1) AM fungal abundance would be greater in “Reference” compared to “Disturbed” areas, and (2) plant functional group cover at the sampling source would help predict AM fungal abundance. Methods At six sites, we sampled soil and measured plant functional group cover from paired areas that had documented disturbance with low native plant cover (“Disturbed”) and no or low disturbance with high native plant cover (“Reference”). We compared the mycorrhizal inoculum potential (MIP), a measure of the density of viable propagules of AM fungi, in these soils using two greenhouse bioassays: one with 120 Bouteloua gracilis plants and the other with 120 Zea mays plants. Results MIP was greater in Reference than Disturbed areas at five of the six sites in the B. gracilis bioassay. Native grass cover was strongly positively correlated with MIP. Conclusions These results suggest that both disturbance and plant functional group can help predict MIP, and that the presence of native grass seems to consistently correlate with MIP across a range of dryland contexts.