Micro-fractionation shows microbial community changes in soil particles below 20 μm

IntroductionMicro-scale analysis of microbes in soil is essential to the overall understanding of microbial organization, interactions, and ecosystem functioning. Soil fractionation according to its aggregated structure has been used to access microbial habitats. While bacterial communities have been extensively described, little is known about the fungal communities at scales relevant to microbial interactions. MethodsWe applied a gentle soil fractionation method to preserve stable aggregated structures within the range of micro-aggregates and studied fungal and bacterial communities as well as nitrogen cycling potentials in the pristine Rothamsted Park Grass soil (bulk soil) as well as in its particle size fractions (PSFs; >250 mu m, 250-63 mu m, 63-20 mu m, 20-2 mu m, <2 mu m, and supernatant). ResultsOverall bacterial and fungal community structures changed in PSFs below 20 mu m. The relative abundance of Basidiomycota decreased with decreasing particle size over the entire measure range, while Ascomycota showed an increase and Mucoromycota became more prominent in particles below 20 mu m. Bacterial diversity was found highest in the < 2 mu m fraction, but only a few taxa were washed-off during the procedure and found in supernatant samples. These taxa have been associated with exopolysaccharide production and biofilm formation (e.g., Pseudomonas, Massilia, Mucilaginibacter, Edaphobaculum, Duganella, Janthinobacterium, and Variovorax). The potential for nitrogen reduction was found elevated in bigger aggregates. DiscussionThe observed changes below 20 mu m particle are in line with scales where microbes operate and interact, highlighting the potential to focus on little researched sub-fractions of micro-aggregates. The applied method shows potential for use in studies focusing on the role of microbial biofilms in soil and might also be adapted to research various other soil microbial functions. Technical advances in combination with micro-sampling methods in soil promise valuable output in soil studies when particles below 20 mu m are included.

Automated summary

Micro-scale analysis of microbes in soil is crucial for understanding microbial organization, interactions, and ecosystem functioning. This study used a gentle soil fractionation method to examine fungal and bacterial communities as well as nitrogen cycling potentials in different particle size fractions. The results showed that microbial community structures changed below 20 μm, suggesting the importance of studying sub-fractions of micro-aggregates to understand microbial interactions.