【目的】 了解西南喀斯特地区不同龄组马尾松(Pinus massoniana)人工林土壤理化性质变化,综合分析地形因子、林分特征及植物多样性指标对土壤性质的影响,为退化喀斯特地区环境治理提供参考。【方法】 在贵州省遵义市凤冈县,选取中龄林、近熟林和过成熟林3个龄组系列共11个马尾松人工林样地,样地按25.82 m×25.82 m方形设置,调查乔木层植物种名、高度及胸径,同时记录样地海拔、坡位、坡度及各样地主要物种组成,在每个样地的西南、西北、东北、东南、中共5个方位设置5个2 m×2 m的灌木样方,调查灌木层植物种名及株数,在每个灌木样方内设置1 m×1 m的草本样方,调查草本层植物种名和盖度,量化马尾松人工林土壤理化性质变化并分析其影响因子。【结果】 不同龄组之间马尾松人工林土壤容重、孔隙度、含水量、有机碳含量、全磷含量均无显著差异(P>0.05),而全氮含量在[0,20)cm土层随林龄的增长呈先升高后降低,碱解氮含量在[20,40)cm土层随林龄的增长逐步降低,速效磷含量在[0,20)cm和[20,40)cm土层随林龄的增长呈先降低后升高的趋势(P<0.05);马尾松人工林土壤容重、孔隙度和含水量在同一龄组[0,20)cm和[20,40)cm的两土层之间均无显著差异(P>0.05),中龄林、近熟林和过成熟林的土壤有机碳含量、近熟林和过成熟林的全氮含量和碱解氮含量、过成熟林的全磷含量和速效磷含量在[0,20)cm和[20,40)cm两土层之间均有显著差异(P<0.05),均随土层的加深而降低;相关性分析表明,地形因子、林分特征和植物多样性指标均是影响马尾松人工林土壤物理性质和养分变化的因素,逐步回归分析显示影响土壤物理性质变化的因素主要是林分密度和植物多样性指标,而地形因子、林分特征和植物多样性均是影响土壤养分的因素。RDA分析表明林分特征解释马尾松人工林土壤理化性质变异的36.60%,植物多样性解释土壤理化性质变异的27.00%,地形因子解释土壤理化性质变异的10.30%。【结论】 龄组变化对马尾松人工林土壤氮磷含量产生了显著影响,马尾松人工林的经营管理过程中应随着马尾松的生长发育适当添加氮肥和磷肥以维持马尾松人工林的生产力和可持续发展,而龄组变化对土壤物理性质没有显著影响,林分密度和树高是影响土壤理化性质变化的主要因子。

【Objective】 The aim of the present study was to investigate the changes of soil physical and chemical properties of Pinus massoniana plantations of different ages in Karst areas in southwest China, as well as comprehensively analyze the effects of topographic factors, stand characteristics and plant diversity on soil properties to provide reference for environmental management in degraded Karst areas.【Method】 In the present study, 11 P. massoniana plantations at three different ages, namely, middle-aged plantation, near-mature plantation, and over-aged plantation, were selected in Fenggang County, Zunyi City, Guizhou Province. The area of the plots was 25.82 m × 25.82 m. The species name, height and diameter at breast height (DBH) of the tree layer were investigated, and the altitude, position, slope and species composition of each plot were recorded. Five 2 m × 2 m shrub quadrats were set up in the southwest, northwest, northeast, southeast and middle areas of each plot to investigate the species name and number of plants in the shrub layer. A 1 m × 1 m herb quadrat was set up in each shrub quadrat to investigate the species name and coverage of herbs. The changes of soil physical and chemical properties were quantified, and the influencing factors were analyzed.【Result】 There were no significant differences in soil bulk density, porosity, water content, organic carbon content and total phosphorus content among the different age groups of the P. massoniana plantations (P>0.05). The total nitrogen content increased initially and then decreased with the increase in plantation age in the 0-20 cm soil layer, and the alkali-hydrolyzable nitrogen content decreased gradually with the increase of plantation age in the 20-40 cm soil layer. Moreover, the available phosphorus content decreased initially and then increased with the increase in plantation age in the 0-20 cm and 20-40 cm soil layers (P<0.05). No significant differences were found in the soil bulk density, porosity, and water content between the 0-20 cm and 20-40 cm soil layers within the same age group (P>0.05). The soil organic carbon content of the three age groups, the total nitrogen content and alkali-hydrolyzable nitrogen content of the near-mature and over-aged plantations, and the total phosphorus and available phosphorus content of the over-aged plantation were significantly different between the 0-20 cm and 20-40 cm soil layers (P<0.05). These contents decreased with the deepening of soil layer. Correlation analysis showed that topographic factors, stand characteristics, and plant diversity were the factors affecting soil physical properties and nutrient changes in the P. massoniana plantations. Stepwise regression analysis showed that stand density and plant diversity were the main factors affecting soil physical properties, while topographic factors, stand characteristics, and plant diversity were the factors affecting soil nutrients. Redundancy analysis (RDA) showed that stand characteristics, plant diversity, and topographic factors explained 36.60%, 27.00% and 10.30% of the variation in the soil physicochemical properties, respectively.【Conclusion】 The plantation age has a significant impact on the soil nitrogen and phosphorus contents of P. massoniana plantations, suggesting that nitrogen fertilizer and phosphorus fertilizer should be added appropriately with the growth and development to maintain the productivity and sustainable development of P. massoniana plantations. Changes in the plantation age has no significant effect on soil physical properties, while the stand density and tree height are the main factors affecting the soil physical and chemical properties in P. massoniana plantations.