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Increased belowground carbon inputs and warming promote loss ofsoil organic carbon through complementary microbial responses

  • Author(s): Hopkins, FM
  • Filley, TR
  • Gleixner, G
  • Lange, M
  • Top, SM
  • Trumbore, SE
  • et al.

Current carbon cycle-climate models predict that future soil carbon storage will be determined by the balance between CO fertilization and warming. However, it is uncertain whether greater carbon inputs to soils with elevated CO will be sequestered, particularly since warming hastens soil carbon decomposition rates, and may alter the response of soils to new plant inputs. We studied the effects of elevated CO and warming on microbial soil carbon decomposition processes using laboratory manipulations of carbon inputs and soil temperature. We incubated soils from the Aspen Free Air CO Enrichment experiment, where no accumulation of soil carbon has been observed despite a decade of increased carbon inputs to soils under elevated CO . We added isotopically-labeled sucrose to these soils in the laboratory to mimic and trace the effects of increased carbon inputs on soil organic carbon decomposition and its temperature sensitivity. Sucrose additions caused a positive priming of soil organic carbon decomposition, demonstrated by increased respiration derived from soil carbon, increased microbial abundance, and a shift in the microbial community towards faster growing microorganisms. Similar patterns were observed for elevated CO soils, suggesting that the priming effect was responsible for reductions in soil carbon accumulation at the site. Laboratory warming accelerated the rate of the priming effect, but the magnitude of the priming effect was not different amongst temperatures, suggesting that the priming effect was limited by substrate availability, not soil temperature. No changes in substrate use efficiency were observed with elevated CO or warming. The stimulatory effects of warming on the priming effect suggest that increased belowground carbon inputs from CO fertilization are not likely to be stored in mineral soils. © 2014 The Authors. 2 2 2 2 2 2 2 2

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