title: Temperature-dependent shift from labile to recalcitrant carbon sources of arctic heterotrophs.
abstract: Soils of high latitudes store approximately one-third of the global soil carbon pool. Decomposition of soil organic matter (SOM) is expected to increase in response to global warming, which is most pronounced in northern latitudes. It is, however, unclear if microorganisms are able to utilize more stable, recalcitrant C pools, when labile soil carbon pools will be depleted due to increasing temperatures. Here we report on an incubation experiment with intact soil cores of a frost-boil tundra ecosystem at three different temperatures (2 degrees C, 12 degrees C and 24 degrees C). In order to assess which fractions of the SOM are available for decomposition at various temperatures, we analyzed the isotopic signature of respired CO2 and of different SOM fractions. The delta13C values of CO2 respired were negatively correlated with temperature, indicating the utilization of SOM fractions that were depleted in 13C at higher temperatures. Chemical fractionation of SOM showed that the water-soluble fraction (presumably the most easily available substrates for microbial respiration) was most enriched in 13C, while the acid-insoluble pool (recalcitrant substrates) was most depleted in 13C. Our results therefore suggest that, at higher temperatures, recalcitrant compounds are preferentially respired by arctic microbes. When the isotopic signatures of respired CO2 of soils which had been incubated at 24 degrees C were measured at 12 degrees C, the delta13C values shifted to values found in soils incubated at 12 degrees C, indicating the reversible use of more easily available substrates. Analysis of phospholipid fatty acid profiles showed significant differences in microbial community structure at various incubation temperatures indicating that microorganisms with preference for more recalcitrant compounds establish as temperatures increase. In summary our results demonstrate that a large portion of tundra SOM is potentially mineralizable.
authors.affiliation: Institute of Ecology and Conservation Biology, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria.
authors.forename: Christina
authors.initials: C
authors.lastname: Biasi
authors.forename: Olga
authors.initials: O
authors.lastname: Rusalimova
authors.forename: Hildegard
authors.initials: H
authors.lastname: Meyer
authors.forename: Christina
authors.initials: C
authors.lastname: Kaiser
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wanek
authors.forename: Pavel
authors.initials: P
authors.lastname: Barsukov
authors.forename: Högne
authors.initials: H
authors.lastname: Junger
authors.forename: Andreas
authors.initials: A
authors.lastname: Richter
mesh_terms: D001110:Arctic Regions; D001673:Biodegradation, Environmental; D018533:Biomass; D002244:Carbon / Q000378:metabolism*; D002245:Carbon Dioxide / Q000378:metabolism; D019069:Cell Respiration; D005591:Chemical Fractionation; D017753:Ecosystem; D005227:Fatty Acids / Q000032:analysis / Q000737:chemistry; D017752:Greenhouse Effect; D012987:Soil / Q000032:analysis*; D012988:Soil Microbiology; D013696:Temperature
chemical_list: D005227:Fatty Acids; D012987:Soil; D002245:Carbon Dioxide; D002244:Carbon