喀斯特山区植被退化过程中的土壤质量变化及评价

为构建喀斯特山区土壤质量评价体系，通过对喀斯特山区植被退化过程中的小生境土壤进行调查，选用土面和石沟2种代表性小生境的土壤作为评价单元，用典范对应分析从29个指标中选出16个，通过因子分析法对土壤质量进行定量综合评价。结果表明:在喀斯特森林植被退化过程中，用土面和石沟2种小生境面积加权计算土壤质量综合分值，能更准确地反映植被退化过程中土壤质量的阶段性变化，具体可分为3个阶段，不同阶段之间土壤活性有机碳、碱解氮、速效磷、速效钾、有效锰、有效硫和脲酶活性出现显著降低，有效铁、蔗糖酶活性和粘粒含量出现显著增加。第Ⅰ阶段内（原生林-次生林）各土壤指标在样地间没有明显的差异；第Ⅱ阶段（灌木林）土壤活性有机碳、碱解氮、速效磷、速效钾、有效硫、脲酶活性和有效锰含量相对第Ⅰ阶段平均分别下降了33.73%、22.41%、57.66%、37.72%、44.59%、46.57%和12.52%；蔗糖酶活性及土壤粘粒含量平均分别增加了81.38%和47.69%；第Ⅲ阶段（灌草丛）土壤速效磷、脲酶活性、碱性磷酸酶活性和有效锰含量相对第Ⅱ阶段平均分别下降了42.82%、44.42%、28.45%和20.55%，土壤有效铁、粘粒含量平均分别增加了56.40%、57.49%，该阶段的土壤速效磷、速效钾含量已处于缺乏的水平，土壤质量明显下降。 

The evaluation of soil quality evolution in the process of vegetation degradation in karst mountain area

To evaluate karst mountain soil quality due to the degradation of vegetation, this paper selected two representative microhabitat soils, i.e. the surface and rocky gully soils, as evaluation units for the construction of karst mountain soil quality evaluation system. 16 indexes were selected from 29 indexes using the canonical correspondence analysis, and the soil quality was discussed by using the comprehensive evaluation method of factor analysis. The results showed that, in the process of vegetation degradation in karst forest, using weighting calculation with the areas of the said two microhabitats to obtain the soil quality synthesis score can more accurately reflect the changes of soil quality due to the vegetation degradation at various phases; and these changes can be specifically divided into 3 phases. During these phases, the concentrations of soil active organic carbon, available N, available P, available K, available Mn, available S and urease all significantly decreased, while the available Fe, sucrase and clay contents significantly increased. In Phase I with vegetation represented by original-secondary forest, no significant difference was found in soil indicators between the sample plots. In Phase II (as represented by shrub wood), the contents of soil active organic carbon, available N, available P, available K, available S and urease and the content of available Mn respectively decreased by 33.73%, 22.41%, 57.66%, 37.72%, 44.59%, 46.57% and 12.52% in average, compared to those of Phase I; and the sucrase activity and soil clay content respectively increased by 81.38% and 47.69% in average. In Phase III (as scrub-grassland soil), the concentrations of soil available P, urease and alkaline phosphatase and available Mn decreased by 42.82%, 44.42%, 28.45% and 20.55%, respectively, compared to Phase II; the content of soil available Fe and clay content respectively increased by 56.40% and 57.49% in average. In this phase, the contents of soil available P and available K become very scarce, which leads to significant decrease of the soil quality.