Elevated Atmospheric Co₂ Levels Impact Soil Protist Functional Core Community Compositions

Area of Science:

• Soil microbiology
• Eukaryotic microbial ecology
• Climate change impacts

Background:

• Protists (microeukaryotes) are key soil microbial players, regulating bacterial populations.
• Atmospheric CO2 enrichment influences bacterial activity, particularly in plant-associated (rhizosphere) soils.
• Understanding protist responses to CO2 is vital for soil ecosystem functioning.

Purpose of the Study:

• To assess the impact of elevated CO2 on soil protist community composition and function.
• To investigate protist-bacteria interactions under varying CO2 levels.
• To analyze microbial community dynamics in bulk and rhizosphere soils.

Main Methods:

• Metabarcoding analysis of 18S rRNA gene sequences from total soil RNA.
• Utilizing data from the Giessen Free-Air CO2 Enrichment (FACE) grassland experiment.
• Comparing protist and bacterial community structures and co-occurrence patterns.

Main Results:

• Elevated CO2 selectively stimulated specific bacterial-feeding protist lineages (ASVs).
• Protist community composition was significantly affected by elevated CO2 (P = 0.006).
• Phagotrophic and parasitic protists showed a slight preference for ambient CO2 conditions.

Conclusions:

• Increased atmospheric CO2 alters soil microeukaryotic communities and their interactions with bacteria.
• Protist-bacteria relationships are predominantly negative, suggesting competitive or predatory dynamics.
• Changes in soil microbial communities under elevated CO2 may have cascading effects on soil food webs.