AUTHOR=Rosado-Porto David , Ratering Stefan , Moser Gerald , Deppe Marianna , Müller Christoph , Schnell Sylvia 

TITLE=Soil metatranscriptome demonstrates a shift in C, N, and S metabolisms of a grassland ecosystem in response to elevated atmospheric CO2

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.937021

DOI=10.3389/fmicb.2022.937021

ISSN=1664-302X

ABSTRACT=<p>Soil organisms play an important role in the equilibrium and cycling of nutrients. Because elevated CO<sub>2</sub> (eCO<sub>2</sub>) affects plant metabolism, including rhizodeposition, it directly impacts the soil microbiome and microbial processes. Therefore, eCO<sub>2</sub> 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<sub>2</sub> enrichment (Gi-FACE) experiment. Results showed changes in the expression of C cycle genes under eCO<sub>2</sub> 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 N<sub>2</sub>O reductase, involved in the last step of the denitrification process, which explains the increase of N<sub>2</sub>O emissions in the Gi-FACE. Also, a shift in nitrate (<inline-formula><mml:math id="M1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula>) metabolism occurred, with an increase in transcript abundance for the dissimilatory <inline-formula><mml:math id="M2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NO</mml:mtext></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow><mml:mrow><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula> reduction to ammonium (<inline-formula><mml:math id="M3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>NH</mml:mtext></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mo>+</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula>) (DNRA) pathway. S metabolism showed increased transcripts for sulfate (<inline-formula><mml:math id="M4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msubsup><mml:mrow><mml:mtext>SO</mml:mtext></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow><mml:mrow><mml:mn>2</mml:mn><mml:mo>-</mml:mo></mml:mrow></mml:msubsup></mml:math></inline-formula>) assimilation under eCO<sub>2</sub> conditions. Furthermore, soil bacteriome, mycobiome, and virome significantly differed between ambient and elevated CO<sub>2</sub> conditions. The results exhibited the effects of eCO<sub>2</sub> on the transcript abundance of C, N, and S cycles, and the soil microbiome. This finding showed a direct connection between eCO<sub>2</sub> and the increased greenhouse gas emission, as well as the importance of soil nutrient availability to maintain the balance of soil ecosystems.</p>