Soil bacterial taxa have important functional roles in ecosystems (e.g., nutrient cycling, soil formation, plant health). Many factors influence their assembly and regulation, with land cover type (e.g., remnant vegetation, agriculture, urban parks) and plant-soil feedbacks being two well studied factors. However, changes in soil bacterial communities in situ over light-dark cycles have received little attention, despite plants and some bacteria having endogenous circadian rhythms that could influence soil bacterial communities. We sampled surface soils in situ across 24-hour light-dark cycles (at 00:00, 06:00, 12:00, 18:00) at two land cover types (remnant vegetation vs. cleared, grassy areas) and applied 16S rRNA amplicon sequencing to investigate changes in bacterial communities. We show that land cover type strongly affected soil bacterial diversity, with soils under native vegetation expressing 15.41-16.42% lower alpha diversity but 4.92-10.67% greater heterogeneity than soils under cleared vegetation. In addition, we report time-dependent and site-specific changes in bacterial network complexity and between 598-922 ASVs showing significant changes in relative abundance across times. Native site node degree (bacterial interactions) at phylum level was 16.0% higher in the early morning hours compared to the afternoon/evening. Our results demonstrate for the first time that light-dark cycles have subtle yet important effects on the composition of soil bacterial communities in situ and that land cover influences these dynamics. We provide a new view of soil microbial ecology and suggest that future studies should consider the time of day when sampling soil bacteria.
