Bryosphere loss impairs litter decomposition consistently across moss species, litter types, and micro-arthropod abundance

The bryosphere (i.e., ground mosses and their associated biota) is a key
driver of nutrient and carbon dynamics in many terrestrial ecosystems, in
part because it regulates litter decomposition. However, we have a poor
understanding of how litter decomposition responds to changes in the
bryosphere, including changes in bryosphere cover, moss species, and
bryosphere-associated biota. Specifically, the contribution of
micro-arthropods to litter decomposition in the bryosphere is unclear.
Here, we used a 16-month litterbag field experiment in two boreal forests
to investigate bryosphere effects on litter decomposition rates among two
moss species (Pleurozium schreberi and Hylocomium splendens), and two
litter types (higher-quality Betula pendula litter and lower-quality P.
schreberi litter). Additionally, we counted all micro-arthropods in the
litterbags and identified them to functional groups. We found that
bryosphere removal reduced litter decomposition rates by 28% and
micro-arthropod abundance by 29%, and led to a colder micro-climate.
Litter decomposition rates and micro-arthropod abundance were uncorrelated
overall, but were positively correlated in B. pendula litterbags.
Bryosphere effects on litter decomposition rates were consistent across
moss species, litter types, and micro-arthropod abundances and community
compositions. These findings suggest that micro-arthropods play a minor
role in litter decomposition in the boreal forest floor, suggesting that
other factors (e.g., micro-climate, nutrient availability) likely drive
the positive effect of the bryosphere on decomposition rates. Our results
point to a substantial and consistent impairment of litter decomposition
in response to loss of moss cover, which could have important implications
for nutrient and carbon cycling in moss-dominated ecosystems.