The concurrent use of novel soil surface microclimate measurements to evaluate CO2 pulses in biocrusted interspaces in a cool desert ecosystem
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Carbon cycling associated with biological soil crusts, which occupy interspaces between vascular plants in drylands globally, may be an important part of the coupled climate-carbon cycle of the Earth system. A major challenge to understanding CO2 fluxes in these systems is that much of the biotic and biogeochemical activity occurs in the upper few mm of the soil surface layer (i.e., the ‘mantle of fertility’), which exhibits highly dynamic and difficult to measure temperature and moisture fluctuations. Here, we report a multi-sensor approach to simultaneously measuring temperature and moisture of this biocrust surface layer (0–2 mm), and the deeper soil profile, concurrent with automated measurement of surface soil CO2 effluxes. Our results illuminate robust relationships between biocrust water content and field CO2 pulses that have previously been difficult to detect and explain. All observed CO2 pulses over the measurement period corresponded to surface wetting events, including when the wetting events did not penetrate into the soil below the biocrust layer (0–2 mm). The variability of temperature and moisture of the biocrust surface layer was much greater than even in the 0–5 cm layer of the soil beneath the biocrust, or deeper in the soil profile. We therefore suggest that coupling surface measurements of biocrust moisture and temperature to automated CO2 flux measurements may greatly improve our understanding of the climatic sensitivity of carbon cycling in biocrusted interspaces in our study region, and that this method may be globally relevant and applicable.
KeywordsBiological soil crusts Carbon cycle Drylands Pulse-dynamic wetting Soil respiration Surface soil moisture
This material is based upon work supported by the U.S. Department of Energy Office of Science, Office of Biological and Environmental Research Terrestrial Ecosystem Sciences Program, under Award Number DE-SC-0008168 and by the U.S. Geological Survey Ecosystem Mission Area. TAM was supported by a National Science Foundation Postdoctoral Research Fellowship in Biology under Grant No. 1402451 and BW by a Paul Crutzen Nobel Laureate Fellowship. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
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