Soil metatranscriptome demonstrates a shift in C, N, and S metabolisms of a grassland ecosystem in response to elevated atmospheric CO.

Soil organisms play an important role in the equilibrium and cycling of nutrients. Because elevated CO (eCO) affects plant metabolism, including rhizodeposition, it directly impacts the soil microbiome and microbial processes. Therefore, eCO directly influences the cycling of different elements in terrestrial ecosystems. Hence, possible changes in the cycles of carbon (C), nitrogen (N), and sulfur (S) were analyzed, alongside the assessment of changes in the composition and structure of the soil microbiome through a functional metatranscriptomics approach (cDNA from mRNA) from soil samples taken at the Giessen free-air CO enrichment (Gi-FACE) experiment. Results showed changes in the expression of C cycle genes under eCO with an increase in the transcript abundance for carbohydrate and amino acid uptake, and degradation, alongside an increase in the transcript abundance for cellulose, chitin, and lignin degradation and prokaryotic carbon fixation. In addition, N cycle changes included a decrease in the transcript abundance of NO reductase, involved in the last step of the denitrification process, which explains the increase of NO emissions in the Gi-FACE. Also, a shift in nitrate ( ) metabolism occurred, with an increase in transcript abundance for the dissimilatory reduction to ammonium ( ) (DNRA) pathway. S metabolism showed increased transcripts for sulfate ( ) assimilation under eCO conditions. Furthermore, soil bacteriome, mycobiome, and virome significantly differed between ambient and elevated CO conditions. The results exhibited the effects of eCO on the transcript abundance of C, N, and S cycles, and the soil microbiome. This finding showed a direct connection between eCO and the increased greenhouse gas emission, as well as the importance of soil nutrient availability to maintain the balance of soil ecosystems.