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 communitiesin 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.
Keywords : bacterial ecology; biodiversity; circadian rhythm;
land cover; soil microbiome