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Drying/rewetting cycles mobilize old C from deep soils from a California annual grassland

  • Author(s): Schimel, JP
  • Wetterstedt, JAM
  • Holden, PA
  • Trumbore, SE
  • et al.
Abstract

We measured the 14C and 13C signatures of CO2 respired from surface and deep soils released through multiple dry/rewetting cycles in laboratory incubations. The C respired from surface soils included components fixed before and after the 1960s. However, that respired from deep soils was derived from organic matter with a mean turnover time estimated in the range of 650-850 years. This reinforces previous research suggesting that a substantial amount of deep soil C is chemically labile but physically inaccessible to microorganisms, but also suggests that substantial amounts of that C may not be so strongly bound to minerals as to be effectively inert, raising the question of why it hasn't already been metabolized. It also demonstrates the contribution of C fixed before the 1960s to CO2 metabolized in the surface soils at this site. © 2011 Elsevier Ltd.

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