Warming decreases desert ecosystem functioning by altering biocrusts in drylands

Warming and precipitation fluctuations are changing desert ecosystems in
global drylands. However, the effects of climate change on keystone
species such as cryptogamic biocrust in drylands remain relatively
under-investigated, even though biocrusts play a vital role in desert
ecosystems. We conducted a long-term experiment (14 years) to
simulate the responses of two main types of biocrusts to warming coupled
with reduction in precipitation that was achieved by open-top chambers
(OTCs) to simulate the predicted warming and precipitation decreasing
under climate change scenario. We also conduct a structural analysis to
evaluate the resulting changes in desert ecosystem functioning (carbon and
nitrogen cycling). Neither warming and corresponding rainfall
reduction treatments had a negative effect on lichen species richness, but
both treatments reduced lichen cover and biomass. The negative effects of
warming on moss-dominated crusts were much greater than those on
lichen-dominated crusts. Although mosses and lichens had varying degrees
of response to warming, the loss of mosses and decreased lichen cover and
biomass, as well as the shortening of the wet time, resulted in a
reduction in carbon and nitrogen fixation, soil enzyme activity and
water-holding capacity of biocrusts and topsoil. These impacts
collectively change the water balance of drylands and weaken the
hydrological and biogeochemical function of biocrusts.  Synthesis
and applications: Results from this long-term experiment suggest that the
ecosystem C and N cycling and water balance of global drylands may be
highly impacted by climate change, in part because of the response of
biocrusts, which contribute an important implication for both dryland
restoration and earth system dynamics.