林窗式疏伐对云杉人工林土壤持水性能的影响

Effects of different sizes of simulated gaps on the soil water-holding capacity of a Picea asperata plantation

选择川西亚高山云杉人工林，模拟自然林窗形成，布置扩展面积分别为小（74m2）、中（109m2）、大（196m2）3个等级的林窗，探索不同疏伐强度对土壤结构及持水性能的影响，并结合细根生物量、土壤有机质含量等参数，试图揭示导致林窗式疏伐后土壤结构及持水性能差异的因素．结果表明，疏伐初期（1年），林窗的形成对表层（0-10cm）土壤的孔隙状况及持水性能没有显著影响；随着时问的演替，各处理土壤结构及持水性能均得到不同程度的改善．疏伐后8年，小林窗、中林窗和大林窗表层土壤的容重较对照分别低17．91％、7．33％和9．24％，其总孔隙度较对照分别高7．16％、2．81％和3．65％，其非毛管孔隙度较对照分别高32．89％、8．16％和15．79％，但不同强度疏伐对土壤持水性能的影响不显著．细根生物量、土壤有机质含量和水占孔隙比是影响土壤物理结构及持水性能的主要因素．上述结果表明随着林窗式疏伐抚育进程的推进，小林窗能显著改善表层土壤结构，但对土壤持水性能方面的影响不显著．（图1表5参56）

This study investigated how gap-model thinning affects soil water-holding capacity, and which factors mediate this influence. To achieve this goal, we applied thinning by simulating gap formation （using four gap sizes of 0, 74, 109, and 196 m2） in a spruce （Picea asperata） plantation in western Sichuan, China. We further analyzed how the fine root biomass and soil organic matter content affected the effects of gap-model thinning on the physical structure and water-holding capacity of the soil. Results showed that in the first year after thinning there were only minor responses of surface soil bulk density, porosity, and water-holding capacity to gap-model thinning. However, as the thinning treatment continued, the soil structure and water- holding capacity continued to improve. Compared to the control, the bulk density of the surface soil decreased by 17.91% in the small gap treatment, 7.33% in the medium gap treatment, and 9.24% in the large gap treatment after eight years of thinning. The total porosity of the surface soil increased by 7.16% in the small gap treatment relative to the control, 2.81% in the medium gap treatment, and 3.65% in the large gap treatment. Additionally, the non-capillary porosity of the surface soil increased by 32.89% in the small gap treatment compared to the control, 8.16% in the medium gap treatment, and 15.79% in the large gap treatment. However, eight years of thinning did not significantly affect the soil water-holding capacity. Correlation analysis showed that the fine root biomass, soil organic carbon content, and water ratio in soil pores were the main factors affecting the soil physical structure and water-holding capacity. Overall, our results showed that the small gap treatment significantly improved the surface soil structure, but had no significant effects on the soil water-holding capacity.