Cheatgrass (Bromus tectorum) invasion alters fire regimes, leading to a grassland vegetation dominated by cheatgrass, replacing natural sagebrush habitat. Restoring cheatgrass invaded grasslands with native species, especially sagebrush (Artemisia tridentata), is very difficult, and restoration success has been limited. Several studies have shown significant changes in some components of the soil microbial community following cheatgrass invasion, suggesting that restoration of soil microbes may promote re-establishment success by native plants. We sampled soil and roots from cheatgrass and sagebrush plants in cheatgrass disturbed and non-disturbed areas in Arizona, Utah and Idaho and used next generation (Illumina) sequencing of bacterial and fungal amplicons to describe the root and rhizosphere soil fungal and bacterial communities. We also conducted a greenhouse experiment to determine if inoculation with soil from undisturbed sagebrush vegetation would improve sagebrush growth in soil from cheatgrass invaded areas.
Results/Conclusions
Cheatgrass invasion had greater effects on root communities than rhizosphere soil communities; the latter showed larger differences among locations than between invaded and non-invaded sites. Within sagebrush roots, fungal communities were more significantly affected by cheatgrass invasion than bacterial communities. The abundance and diversity of arbuscular mycorrhizal fungi (AMF) was higher in sagebrush roots from native habitat than cheatgrass invaded habitat while the opposite was true for dark septate fungi (DSF). The fungal OTU composition of sagebrush roots was also affected by cheatgrass invasion. Although cheatgrass roots had low diversity of AMF and high diversity of DSF, similar to sagebrush roots in cheatgrass invaded areas, their fungal OTU composition was distinct. Inoculation of cheatgrass affected soil with a small amount of soil from sagebrush dominated areas had inconsistent effects on sagebrush growth that depended on sagebrush seed and inoculum source populations. Taken together, these results show that cheatgrass invasion significantly altered the root associated fungal communities of sagebrush. However, the distinct communities of roots and rhizosphere soil, and the preliminary results of greenhouse inoculation experiments, suggest that inoculation with soil from intact sagebrush may not restore microbial communities and their function following cheatgrass invasion.