喀斯特峰丛洼地不同生态系统的土壤肥力变化特征

基于喀斯特峰丛洼地坡耕地、草丛、灌丛、人工林、次生林、原生林6种典型生态系统的土壤主要养分、矿质养分和微生物这3组变量共计20个指标的调查、取样和分析，运用多重比较分析、主成分分析和典范相关分析探讨了其土壤肥力变化特征、主要影响因子及两两之间的相互关系。结果表明，喀斯特峰丛洼地土壤pH值为6.60—7.75，土壤主要养分、微生物种群数量和微生物生物量明显高于同纬度地区地带性红壤，矿质养分含量相对较低，其中SiO2、Al2O3、Fe2O3占矿质全量的90%以上。土壤肥力的总体趋势为原生林>次生林>灌丛>草丛>坡耕地>人工林。喀斯特石漠化地区实行林草结合的退耕还林还草模式更有利于土壤生态系统的环境改善，坡耕地应多施有机肥和氮肥，人工林应多施氮肥。原生林植物与养分之间达到了良好的平衡状态，主要应加强森林抚育管理，改善森林环境，保障植物、土壤养分及微生物之间的良好协调关系。确保土壤资源的合理利用，促进喀斯特峰丛洼地乃至整个西南喀斯特区域植被的迅速恢复和生态重建。

Characteristics of soil fertility in different ecosystems in depressions between karst hills

The main soil nutrients, soil mineral nutrients, and soil microbes were investigated, sampled, and analyzed in farmland, grassland, scrub, plantation forest, secondary forest, and primary forest in depressions between karst hills. Multiple comparison analysis, principal component analysis, and canonical correlation analysis were used to study the soil characteristics and the main factors affecting soil fertility as well as the relationships between those three factors: the main soil nutrients, soil mineral content, and soil microbes. Soil pH ranged from 6.60 to 7.75 in depressions between karst hills. Across the different ecological systems, from farmland to primary forest soil, pH varied from acidic to alkaline. The soil nutrient content varied in different ecological systems, and changes in soil nutrient content can be modeled during the process of ecological succession. In the process of secondary succession soil organic matter (SOM), total nitrogen (TN), total phosphorous (TP), available nitrogen (AN), and available phosphorous (AP) content increased gradually. The soil nutrient levels were highest in primary forest and follow the sequence of primary forest > secondary forest > shrub > grassland. The soils of these habitats were all significantly or very significantly different. When the landuse type was changed from a landscape with natural secondary succession to farmland or plantation forests, soil TP and TK content increased significantly. The content of the main soil nutrients (SOM, TN, TP, TK, AN, AP, AK), microbial populations, and the soil content of C, N, and P in microbial biomass (Cmic, Nmic, Pmic, respectively), were obviously higher in the karst area than that in the red soil region at the same latitudes. The content of mineral nutrients was relatively low and the sum of SiO2, Al2O3, and Fe2O3 accounted for more than 90% of the total mineral nutrients. Although the supply of Ca and Mg were adequate, serious shortages of other mineral nutrients limited plant growth and development. Many types of ecological systems in depressions between karst hills were not obviously showing signs of rocky desertification, although a strong potential for rocky desertification still exists. All ecosystems studied here had high soil microbial populations, and primary forest had highest total microbial populations, bacteria populations and Actinomyces population while plantation forest had the lowest. Soil fertility can be ranked in the order of primary forest > secondary forest> scrub > grassland > farmland > plantation forest. The landscape in this karst area is strongly heterogeneous; the ecological systems are complex because numerous factors affect the ecosystems and different ecological systems are influenced by different factors. Therefore, the practice of returning farmland to forests or grassland tends to improve the soil ecosystem environment in karst areas which have undergone rocky desertification. Farmland requires more organic and nitrogenous fertilizers and plantation forests require more nitrogenous fertilizer than other ecosystems. In the primary forest, plants and soil nutrients reach a state of dynamic equilibrium, and land management should focus on strengthening and improving the forest environment and balancing the relationships among plants, soil nutrients and microbes. Assuring that soil resources are used rationally will be helpful in improving the results of ecological restoration and accelerate vegetation rehabilitation in depressions between karst hills or even in the entire karst region of southwest China.