关键词: 喀斯特, 马尾松人工林, 土壤理化性质, 土壤养分, 地形因子, 林分特征, 植物多样性

Abstract:

【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.

Key words: Karst, Pinus massoniana plantation, soil physical and chemical properties, soil nutrient, topographic factors, stand characteristics, plant diversity