Abstract:Labile soil organic carbon (LOC) is an indicator in terms of evaluating soil organic matter quality and dynamics. Fractionation of soil organic matter (SOM) implies the separation of the total SOM into different soil physical fractions that are thought to be functionally homogeneous with respect to physicochemical properties and turnover rate, and the organic matter dynamics based on turnover time will be further understood. In this paper, Labile soil organic carbon, evaluated by three indicators obtained from oxidation and physical fractionation methods, was found varies with vegetation types (Mountainous evergreen broad-leaved forest, mixed evergreen and deciduous broadleaved forest, deciduous broad-leaved forest, mixed coniferous and broadleaved forest, sub-alpine dark coniferous forest) distributed along an elevation gradient. A 333mM KMnO4-chemical oxidation method was used to determine the easily oxidized carbon (EOC), and another two physical methods including wet sieving through a 0.053 mm sieve and flotation in aqueous NaI (1.8g?cm-3) were used to determine the particulate organic matter carbon (POC) and light fraction organic carbon (LFOC) respectively.
POC and LFOC contents as well as their proportions decrease with the increasing soil depth, similar result was found in EOC content, while there is no decrease in the proportion of EOC. Compared with lower-elevation vegetation types, higher ones were found significantly higher in their LOC content and proportion. EOC and POC show positive correlations with LFOC (P<0.05), indicates the similar origin of EOC, POC and LFOC. In contrast, negative correlation between LOC and silt+clay(%) content indicates that more LOC are contained in the macroaggregate. EOC, POC and LFOC contents of surface soil layer as well as their proportions decrease with mean annual temperature (MAT), however, no significant was found for the fewer samplings. And a marginal positive correlation was found between MAT and the rate constant for C transfer from the unprotected to the protected soil pool (K) (P=0.062).