The synergistic effects of a leaf mixture on decomposition change with a
period of terrestrial exposure prior to immersion in a stream
Abstract
The effect of mixing litter on decomposition has received considerable
attention in terrestrial and aquatic (but rarely in both) ecosystems,
with a striking lack of consensus in the obtained results. We studied
the decomposition of a mixture of poplar and alder in three
terrestrial:aquatic exposures to determine (1) if the effect of mixing
litter on mass loss, associated decomposers and detritivores differs
between the stream (fully aquatic exposure) and when litter is exposed
to a period of terrestrial exposure prior to immersion and (2) the
global effect of the mixture across exposure scenarios. The effect of
the mixture was additive on mass loss and synergistic on decomposers and
detritivores across exposure scenarios. Within scenarios, mass loss and
decomposers showed synergistic effects only in the fully aquatic
exposure, detritivores showed synergistic effects only when the period
of terrestrial was shorter than the period of aquatic exposure, and when
the period of terrestrial was equal to the period of aquatic exposure
the effect of the mixture was additive on mass loss, decomposers, and
detritivores. The species-specific effects also differed among exposure
scenarios. Alder affected poplar only when there was a period of
terrestrial exposure, with increased sporulation rates and fungal
richness in exposure 25:75, and increased mass loss in exposure 50:50.
Poplar affected alder only under fully aquatic exposure, with increased
mass loss. In conclusion, the synergistic effects of the mixture changed
with a period of terrestrial exposure prior to immersion. These results
provide a cross-boundary perspective on the effect of mixing litter,
showing a legacy effect of exposure to terrestrial decomposition on the
fate of plant litter in aquatic ecosystems and highlighting the
importance of assessing the effect of mixing litter on the associated
biota and not only on mass loss.