Five ways soil bacteria and archaea respond to nematode grazing

Microbial communities in soil ecosystems are shaped by trophic interactions. However, this impact is not well investigated and quantified so far. We analyzed how trophic interactions modulate the bacterial community composition within a natural soil community. The experiment was set up in a microcosm system with circulating airflow filled with haplic cambisol soil, inoculated with maize litter, a bacterivorous nematode, and incubated for 32 days. Soil respiration and total bacterial and archaeal communities were determined at days 0, 4, 8, 16 and 32. Bacterial and archaeal communities were compared through 16S rRNA gene amplicon sequencing and qPCR analysis. Treatments with the bacterivorous nematode resulted in an earlier onset of soil respiration and a strong microbial community shift during the first 16 days. In total, 221 dominant amplicon sequence variants (ASVs) were underlying these community shifts and could be grouped into five distinct response types at the population level. Response types ranged from steadily decreasing over intermitted population maxima to steadily increasing. Taxonomic affiliation was not a factor that distinguished response types. Our results are an important step forward to disentangle microbial population dynamics in response to nematode grazing.