Abstract. Biological soil crusts (biocrusts) are predicted to be
sensitive to the increased temperature and altered precipitation associated
with climate change. We assessed the effects of these factors on soil carbon
dioxide (CO2) balance in biocrusted soils using a sequence of
manipulations over a 9-year period. We warmed biocrusted soils by 2 and,
later, by 4 ∘C to better capture updated forecasts of future
temperature at a site on the Colorado Plateau, USA. We also watered soils to
alter monsoon-season precipitation amount and frequency and had plots that
received both warming and altered precipitation treatments. Within treatment
plots, we used 20 automated flux chambers to monitor net soil exchange (NSE)
of CO2 hourly, first in 2006–2007 and then again in 2013–2014, for a
total of 39 months. Net CO2 efflux from biocrusted soils in the warming
treatment increased a year after the experiment began (2006–2007). However,
after 9 years and even greater warming (4 ∘C), results were more
mixed, with a reversal of the increase in 2013 (i.e., controls showed higher
net CO2 efflux than treatment plots) and with similarly high rates in
all treatments during 2014, a wet year. Over the longer term, we saw
evidence of reduced photosynthetic capacity of the biocrusts in response to
both the temperature and altered precipitation treatments. Patterns in
biocrusted soil CO2 exchange under experimentally altered climate
suggest that (1) warming stimulation of CO2 efflux was diminished later
in the experiment, even in the face of greater warming; and (2) treatment
effects on CO2 flux patterns were likely driven by changes in biocrust
species composition and by changes in root respiration due to vascular plant
responses.
Spatial and temporal patterns of biophysical variables and their influence on CO2 flux in a high arctic wetland