2012年后新成立研究组知识库

Land-use changes accompanying revegetation improve the sequestration of soil organic carbon (SOC) by accelerating aggregate formation. However, the intrinsic mechanisms of long-term C flow and sequestration following land-use changes in karst ecosystems remain largely unclear. We examined variations in aggregate- associated OC fraction and C flow pathways across four karst land uses (cropland, grassland, shrubland, and forestland). Result showed that agricultural cultivation disrupted soil aggregates and contributed to SOC depletion. Aggregate stability, labile and recalcitrant OC stocks generally increased along the vegetation restoration. The OC contents of bulk soils exhibited a strong positive correlation with the OC contents and mass proportions of macro- and micro-aggregates. Proportions of labile organic carbon (LOC) to SOC in the topsoil reduced with decreasing aggregate sizes, with being reshaped C pool by increasing LOC fraction in cropland. The delta 13 C values of bulk soil decreased with the sequence of vegetation restoration, indicating a decreasing turnover rate and C loss as land cover shifts from grass to forest. The delta 13 C was enriched as aggregate size decreased, with maximum value (-14.59 parts per thousand) in the silt + clay fraction under grassland at the soil depth of 10-20 cm. Soil aggregate-associated C flow pathways predominantly occurred from macroaggregates to microaggregates and silt + clay size classes. This indicates that litter C input was incorporated into macroaggregates that were formed initially, while old SOC was often deposited in silt + clay fractions. Cropland demonstrated a greater intensity of C flows in topsoil compared to other land-use types, reflecting the fast turnover rate and loss of C under cropland soils. These results highlight that long-term soil labile and recalcitrant OC pools and C stabilization mechanisms at aggregate level are largely affected by land use. Appropriate land-use associated with grass and forest restoration maybe a promising way for enhancing SOC sequestration in karst areas.