重庆酸雨区马尾松纯林改造对土壤酸化特征及团聚体稳定性的影响

马尾松对酸沉降危害极其敏感，生产实践中往往通过林分改造来应对酸沉降危害。为掌握酸雨区马尾松纯林改造对土壤酸化环境的影响及科学指导经营管理，采用空间代替时间的方法，对重庆铁山坪林场的马尾松纯林及其阔叶化改造后的香樟林、木荷林、马尾松×香樟混交林和马尾松×木荷混交林土壤养分、酸化特征及团聚体稳定性进行研究。结果表明：（1）除木荷混交林的腐殖质层土壤有机碳和全氮含量显著增加外，其他森林类型总体均减少（P<0.05）；香樟林及其混交林的各层土壤全磷和全钾含量均增加，但木荷林及其混交林均减少（P<0.05）。（2）改造为香樟林及其混交林能显著提高土壤pH值、交换性盐基离子含量和盐基饱和度，降低交换性Al³⁺含量，但改造为木荷林及其混交林则总体对土壤酸化特征影响不明显（P>0.05）。（3）木荷林及其混交林淀积层的水稳性大团聚体含量增加，香樟林及其混交林则是微团聚体含量增加（P<0.05）。（4）改造对各森林类型腐殖质层和木荷林淋溶层及淀积层的土壤团聚体稳定性均无显著影响，但能增强马尾松混交林和香樟林淋溶层或淀积层的土壤团聚体稳定性（P<0.05）。综合来看，改造能改变土壤酸化环境，但各森林类型的影响不同，改造为香樟林或其混交林的改善效果总体好于木荷林或其混交林。因而对酸雨区马尾松纯林改造，还应根据改造树种特性及林分特征，科学确定相应的改造方法，尤其应注重改造林分的全过程抚育经营，以营造良好的林下环境。

Effects of transformation of Masson pine forest on characteristics of soil acidification and aggregate stability within polluted areas of Chongqing

Soil acidification is a formidable environmental issue which acts as a driver of change to alter forest tree species community composition over time. Forests characterized by the dominant tree species, Pinus massoniana, have shown extreme sensitivity to the increased soil acidity and are undergoing transformational shifts in community composition as a response. Planting treatments are a strategy often used to mitigate the harmful effects of increasing soil acidity, though little is known about how different treatments may affect soil physicochemical properties in P. massoniana forests. In this study, we characterized soil nutrient levels, stable soil aggregates, and soil acidification status of five different forest types (including pure stands of P. massoniana, Cinnamomum camphora, Schima superba and mixed stands of C. camphora-P. massoniana, S. superba-P. massoniana) to show how shifts in community composition may affect soil quality and help to inform management in areas impacted by acid rain. We collected and analyzed soil samples from O, A, and B horizons at 10 points within 20 m×20 m plots replicated 3-4 times within each forest type. For O horizon soils, organic carbon and total nitrogen were lower in all forest types (P<0.05) compared to those measured in stands of pure P. massoniana, with the exception of mixed stands of S. superba-P. massoniana. Total phosphorus and total potassium levels were greater in C. camphora and mixed C. camphora-P. massoniana stands as compared to pure P. massoniana for all horizons, while pure S. superba and mixed S. superba-P. massoniana stands showed significantly lower amounts (P<0.05). Our findings suggest that planting C. camphora may improve soil acidification status, while planting S. superba is unlikely to have a significant effect (P>0.05). Stable soil macro aggregates were greater in B horizon soils of pure S. superba and mixed S. superba-P. massoniana stands, while micro aggregate abundances were greater in pure C. camphora and mixed C. camphora-P. massoniana stands (P<0.05) compared to pure stands of P. massoniana. Soil aggregate stability showed no significant differences in O horizon soils across all forest types or A and B horizon soils from pure S. superba stands, though stability was greater in A and B horizon soils from mixed P. massoniana stands and pure stands of C. camphora (P<0.05) as compared to pure P. massoniana stands. In conclusion, different tree planting treatments demonstrated ability to alter soil acidification status within a P. massoniana plantation, though the effects of different treatments varied. Further study is needed to determine the most effective management strategies for restoring acid-polluted forest sites.