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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 15, issue 14 | Copyright
Biogeosciences, 15, 4561-4573, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 26 Jul 2018

Research article | 26 Jul 2018

Patterns of longer-term climate change effects on CO2 efflux from biocrusted soils differ from those observed in the short term

Anthony Darrouzet-Nardi1, Sasha C. Reed2, Edmund E. Grote2, and Jayne Belnap2 Anthony Darrouzet-Nardi et al.
  • 1University of Texas at El Paso, 500 W. University Ave., El Paso, TX 79912, USA
  • 2U.S. Geological Survey, Southwest Biological Science Center, Moab, UT 84532, USA

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.

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Biocrusts are photosynthetic communities on the surface of many desert soils. We investigated the response of biocrusts and the soil beneath them (including plant roots) to 9 years of simulated warming and changing precipitation patterns. We monitored the exchange of carbon between soil and atmosphere using automated chambers. As plants and biocrusts responded negatively to the treatments, we saw reduced photosynthesis in biocrusts but variable overall carbon exchange over 9 years.
Biocrusts are photosynthetic communities on the surface of many desert soils. We investigated...