Elevated Atmospheric CO Modifies Mostly the Metabolic Active Rhizosphere Soil Microbiome in the Giessen FACE Experiment.

Elevated levels of atmospheric CO lead to the increase of plant photosynthetic rates, carbon inputs into soil and root exudation. In this work, the effects of rising atmospheric CO levels on the metabolic active soil microbiome have been investigated at the Giessen free-air CO enrichment (Gi-FACE) experiment on a permanent grassland site near Giessen, Germany. The aim was to assess the effects of increased C supply into the soil, due to elevated CO, on the active soil microbiome composition. RNA extraction and 16S rRNA (cDNA) metabarcoding sequencing were performed from bulk and rhizosphere soils, and the obtained data were processed for a compositional data analysis calculating diversity indices and differential abundance analyses. The structure of the metabolic active microbiome in the rhizospheric soil showed a clear separation between elevated and ambient CO (p = 0.002); increased atmospheric CO concentration exerted a significant influence on the microbiomes differentiation (p = 0.01). In contrast, elevated CO had no major influence on the structure of the bulk soil microbiome (p = 0.097). Differential abundance results demonstrated that 42 bacterial genera were stimulated under elevated CO. The RNA-based metabarcoding approach used in this research showed that the ongoing atmospheric CO increase of climate change will significantly shift the microbiome structure in the rhizosphere.