Abstract
Elevated levels of atmospheric CO2 lead to the increase of plant photosynthetic rates, carbon inputs into soil and root exudation. In this work, the effects of rising atmospheric CO2 levels on the metabolic active soil microbiome have been investigated at the Giessen free-air CO2 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 CO2, 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 CO2 (p = 0.002); increased atmospheric CO2 concentration exerted a significant influence on the microbiomes differentiation (p = 0.01). In contrast, elevated CO2 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 CO2. The RNA-based metabarcoding approach used in this research showed that the ongoing atmospheric CO2 increase of climate change will significantly shift the microbiome structure in the rhizosphere.
Highlights
The rise of atmospheric carbon dioxide (CO2) concentrations and global warming are well-documented processes
In regard to alpha diversity of rhizosphere and bulk soil fractions from aCO2 rings, significantly higher diversity values were observed in bulk compared to rhizosphere soils with Observed species (p value 0.00036), Shannon (p value 0.0086), and Fisher (p value 0.00036) indexes (Fig. 1)
Our results showed that e CO2 had a strong effect in the Giessen free-air CO2 enrichment (Gi-free-air C O2 enrichment (FACE)) on the metabolic active microbiome of the rhizosphere soil, in contrast to the microbiome of the bulk soil which remained mostly unaffected
Summary
The rise of atmospheric carbon dioxide (CO2) concentrations and global warming are well-documented processes. Considering that nearly up to 21% of all photosynthetically fixed carbon is transferred to the rhizosphere, roots and root exudates influence the composition and biomass of soil microbiome [10, 11]. Elevated atmospheric CO2 increases efflux amounts of total soluble sugars, amino acids, phenolic acids, and organic acids in the root exudates [12,13,14]. The rates of organic carbon as energy sources enhance microbial degradation of soil organic matter (SOC), known as priming effect [14]. Priming effect is defined as an accelerated decomposition of SOC due to an increased supply of labile C to the soil and changes in the microbial activity as a response [15]. The microbial succession is accompanied by the activation of various, previously
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