Abstract
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.