以坡耕地为对照,研究了喀斯特峰丛洼地任豆、香椿、板栗、柑橘、任豆+桂牧1号、桂牧1号和撂荒7种常见退耕还林还草模式下土壤微生物种群数量、微生物量碳氮磷及其分形特征和主要土壤酶活性特征。结果表明,不同退耕还林还草模式土壤微生物种群数量组成不同,除任豆模式外其他退耕还林还草模式均能提高土壤微生物总数量;不同退耕还林还草模式(除任豆模式外)土壤微生物量碳(MB<sub>C</sub>)含量极显著增加,撂荒地最高,土壤微生物量氮(MB<sub>N</sub>)含量变化范围不大,呈下降趋势,土壤微生物量磷(MB<sub>P</sub>)含量的变异很大,香椿、板栗、撂荒和桂牧1号模式显著或极显著高于坡耕地;土壤MB<sub>C</sub>与细菌数量的关系最相关(<em>D=</em>-4.07,<em>R</em>=0.81,<em>P</em><0.01),其次为MB<sub>C</sub>与放线菌数量(<em>D</em>=3.82,<em>R</em>=0.44,<em>P</em><0.05),再次为MB<sub>N</sub>与真菌数量(<em>D</em>=0.58,<em>R</em>=0.61,<em>P</em><0.01),MB<sub>C</sub>与真菌数量、MB<sub>N</sub>与细菌、放线菌数量以及MB<sub>P</sub>与细菌、真菌、放线菌数量之间不存在分形关系;不同退耕还林还草模式(除桂牧1号模式外)均显著或极显著增加了土壤蔗糖酶、脲酶和磷酸酶活性。总之,不同退耕还林还草模式均改善了土壤微生物特性,为喀斯特峰丛洼地脆弱生态系统恢复与重建提供了重要依据。;Soil microbial life <em>in vivo</em> is a major component of soils throughout the whole process of soil development. The living environment for soil microorganisms is a very sensitive early-warning indicator of change in soil ecosystems. Using slope cropland as a contrast, we investigated the main soil microbial populations, microbial biomass carbon (MB<sub>C</sub>), nitrogen (MB<sub>N</sub>), and phosphorus (MB<sub>P</sub>) and their fractal characteristic model, as well as soil enzyme activities under seven grain-for-green patterns (cultivation of <em>Zenia insignis</em>, <em>Toona sinensis</em>, <em>Castanea mollissima</em>, <em>Citrus reticulate</em>, <em>Zenia insignis</em> + Guimu No. 1 forage, Guimu No. 1 forage, and abandoned cropland) in depressions between karst hills. The main soil microbial populations differed under different grain-for-green patterns. Actinomycetes were 71.28% to 96.44% of the microbial population in the slope cropland, <em>Zenia insignis</em> + Guimu No. 1, Guimu No. 1, and abandoned cropland. Differences in their populations covered up to three orders of magnitude. Bacteria dominated in the other four soils, being 55.24% to 71.79% of the microbial population, but fungi were less than 1%. Bacteria were highest under Guimu No. 1 and abandoned cropland, and were lowest in the slope cropland. Fungi populations were in the order: abandoned cropland > <em>Zenia insignis</em> > Guimu No. 1 > <em>Citrus reticulate</em> > <em>Castanea mollissima</em> > slope cropland > <em>Toona sinensis</em> > <em>Zenia insignis</em> + Guimu No. 1<em>,</em> with significant differences between them. All the grain-for-green patterns except <em>Zenia insignis</em> increased total soil microbial populations. The differences between Guimu No. 1, abandoned cropland, and <em>Zenia insignis</em> + Guimu No. 1 were significant (<em>P</em><0.05), and were significantly higher than the others. Microbial biomass carbon (MB<sub>C</sub>) in the all grain-for-green patterns except <em>Zenia insignis</em> was significantly higher than in the slope cropland, and was highest in the abandoned cropland. Microbial biomass nitrogen (MB<sub>N</sub>) varied within a small range, showing a downward trend. Differences in MB<sub>N</sub> between cultivation of <em>Zenia insignis</em> + Guimu, <em>Citrus reticulata</em>, <em>Zenia insignis</em> and slope cropland were significant (<em>P</em><0.05). Microbial biomass phosphorus (MB<sub>P</sub>) varied widely in <em>Toona sinensis</em>, <em>Castanea mollissima</em>, abandoned cropland and Guimu No. 1 but was significantly higher than in slope cropland. MB<sub>C</sub> was well correlated with bacteria (<em>D=</em>-4.07, <em>R</em>=0.81, <em>P</em><0.01), followed by the correlation between MB<sub>C</sub> and actinomycetes (<em>D</em>=3.82, <em>R</em>=0.44, <em>P</em><0.05) and that between MB<sub>N</sub> and fungi (<em>D</em>=0.58, <em>R</em>=0.61,<em> P</em><0.01). However, there was no fractal relationship between the other microbial biomass and microbial populations. Compared with the slope cropland, all the grain-for-green patterns except Guimu No. 1 forage significantly increased the activities of soil sucrase, urease and phosphatase, suggesting an increase in carbon and nitrogen cycling. Under different grain-for-green patterns, the activity of soil sucrase was highest under <em>Toona sinensis</em>, reaching (29.10±7.73) mg g<sup>-1</sup> d<sup>-1</sup>, while the activity of soil urease was highest in the abandoned cropland, reaching (540.7±34.77) μg g<sup>-1</sup> d<sup>-1</sup>, and the activity of soil phosphatase was highest under <em>Castanea mollissima</em>, reaching (991.1±76.28) μg g<sup>-1</sup> d<sup>-1</sup>. All the grain-for-green patterns improved soil microbial properties, suggesting important benefits arising from fragile ecosystem restoration and reconstruction in depressions between karst hills.