| 摘 要： |
Soil organic carbon (SOC) sequestration is closely linked to global climate change and soil quality. Secondary succession of agricultural abandonment under the Grain for Green Project (GGP) program generally promotes SOC sequestration in the karst region of southwestern China. This study investigated the controlling mechanism of enhancing SOC sequestration during secondary succession of agricultural abandonment, based on soil aggregation, soil erosion, and soil Ca dynamic. In the study area, croplands, shrub-grass lands, and secondary forest lands were regarded as the three stages during the secondary succession of cropland abandonment by the space-for-time substitution method. The proportions of water-stable and different-sized aggregates, SOC contents associated with aggregates, soil Ca contents and Ca/Al ratios, and soil erodibility K factors were analyzed in the soils at the 0-10, 10-20, and 20-30 cm depths. The proportions of macro-aggregates at the 0-10 cm depth in the croplands (mean 61.3%) were significantly lower than those in the shrub-grass lands (mean 78.5%) and secondary forest lands (mean 81.6%). The SOC contents associated with macro-aggregates at the 0-20 cm depth in the croplands (mean 30.5 g kg(-1)) were significantly lower than those in the secondary forest lands (mean 52.2 g kg(-1)) but were slightly (not significantly) lower than those under the shrub-grass lands (mean 38.6 g kg(-1)). Soil Ca/Al ratios at the 0-20 cm depth in the croplands (mean 0.087) and shrub-grass lands (mean 0.105) were significantly lower than those under the secondary forest lands (mean 0.63). The proportions of water-stable aggregates increased and the K factor decreased after cropland abandonment. These results indicated that under the experiment conditions, soil aggregation increased, soil erosion reduced, and soil Ca accumulated during the secondary succession of agricultural abandonment. A conceptual model for enhancing SOC sequestration during the secondary succession of agricultural abandonment was proposed. This conceptual model suggests that the GGP program has a positive effect on SOC sequestration and soil quality in the karst region. |
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