Multiple global change factors cause declines of a temperate bryophyte

Climate changes, nutrient enrichment, or land use have been predicted to
affect bryophytes, yet factorial experiments on their effects are missing.
We hypothesised that future climatic conditions, intense grazing, light
limitation, nutrient enrichment have negative effects on the survival and
photosynthetic condition of a common temperate bryophyte, and their joint
effects become strong even if individual factors have only weak effects.
We tested the effects of future climatic conditions, grazing, light
limitation, and nutrient on a common temperate bryophyte (Brachythecium
rutabulum) as well as the multiple stress hypothesis. We measured biomass
and chlorophyll fluorescence of transplanted moss colonies after two
growing seasons’ full-factorial treatments of fertilization, exclusion of
sheep grazing, and light addition by LED lamps, replicated in ambient and
future climate conditions arranged in a global change experimental
facility. Future climate and fertilization had negligible effects on
colony biomass and chlorophyll fluorescence of bryophyte colonies, whereas
light addition and grazing exclusion had positive effects. Colony biomass
and chlorophyll fluorescence decreased with the increasing number of
global change factors. Supporting the multi-stress hypothesis, the effects
of individually weak global change factors on bryophytes can become strong
under multiple global change factors operating in concert.