摘要：

Binding of soil organic matter (OM) at micropore entrances within small mesopores (2-10 nm) has been suggested as a potential mechanism for the stabilization of OM against biodegradation. We hypothesized that the mineral-associated fraction of stable OM [OM resisting treatment with 6% sodium hypochlorite (NaOCI) and subsequently extracted by 10% hydrofluoric acid] is associated with pores < 10 nm in 12 acid subsoil horizons. To study the coverage of micropores by stable OM sorbed in mesopores, we assumed that most micropores have entrances of mesopore size. We compared the accessibility of CO2 at 273 K to micropores after NaOCI treatment with that of NZ at 77 K. In contrast to NZ, diffusion of COZ into micropores is little affected by OM and the difference in both micropore volumes (MIV) is taken as a measure of micropore clogging and thus of the association of stable OM with mesopores. The MIV measured by CO2 adsorption was corrected for Cot sorption in OM (MIV-CO2corr). In 7 out of 12 samples, the MIV-CO2corr equaled the MIV NZ, suggesting that micropore entrances are not blocked by stable OM. For four samples the results were ambiguous, whereas in an Eutric Hapludand Bw horizon, a threefold larger MIV-CO2corr compared with the MIV-N(2)indicates that stable OM was associated with pores < 10 nm. Based on the findings that (i) mineral MIVs derived from CO2 and N-2 adsorption were similar for most samples after exposure to NaOCI, (ii) the change of MIV-N-2 on NaOCI treatment was small in all samples, and (iii) no relationship existed of the MIV-CO2corr and small mesopore volume with the content of mineral-associated stable organic C (OC), we conclude that the association of OM with micropore entrances in small mesopores does not primarily control the stabilization of OM in these acid subsoils.

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