亚热带森林转换对土壤团聚体稳定性的影响

Effects of Subtropical Natural Forest Conversion on Soil Aggregate Stability

森林转换是影响土壤结构稳定性的重要因素。运用干、湿筛两种方法比较研究亚热带天然林转换为人工林后土壤团聚体粒径分布以及团聚体稳定性各个指标MWD(平均重量直径)、GMD(几何平均直径)和PAD(团聚体破坏率)在不同林型间的差异。结果表明:(1)干筛处理下两个林分全土层团聚体以>2 mm粒径为主,湿筛处理下粒径以0.25~2 mm为主。干筛处理天然林0~10 cm土层处>2 mm团聚体约占60%,人工林约占55%;湿筛处理下天然林0~10 cm土层处>2 mm团聚体约占45%,人工林约占23%。转换为人工林后>2 mm团聚体在0~10 cm土层处占比显著降低(P<0.05),降幅达58.18%。(2)干筛处理下不同森林类型相同土层的MWD和GMD值均无显著的差异(P>0.05);湿筛处理下天然林MWD、GMD值在所有土层均高于人工林,且该土层MWD值和GMD值在森林转换后下降幅度最大,分别达到45%和50%。团聚体PAD值变化范围在天然林中为11.07%~30.68%;在人工林中为15.17%~33.46%,森林转换后PAD值在0~10 cm土层显著增加72.91%(P<0.05)。(3)从母岩角度整合相关的研究发现:森林转换后MWD值在沉积岩发育的土壤中下降幅度最大。研究发现:森林转换对团聚体在全土层的粒径分布和稳定性的影响在不同的筛分方法之间得到的结果并不一致,表现为在不同的筛分方法处理下不同森林类型的不同团聚体粒径在全土层中的占比以及NWD、GMD和PAD指标在土层中的变化趋势存在差异。此外,0~10 cm表土的结构稳定性与土壤抗侵蚀能力密切相关,除森林转换对表土团聚体稳定性产生影响外,不同的团聚体筛分方法和母岩性质的差异也会对森林转换后表土的稳定性研究结果产生影响。

Forest conversion is an important factor affecting the stability of soil structure.The particle size distribution of soil aggregates and the aggregate stability indexes MWD(Mean Weight Diameter),GMD(Geometric Mean Diameter)and PAD(the soil of Percentage of Aggregate Destruction)in different forest types were studied by dry and wet screening methods.The results showed that,(1)the aggregate size of the whole soil layer of the two stands was>2 mm under dry screening treatment,and 0.25~2 mm under wet screening treatment.The aggregates>2 mm in 0~10 cm soil layer of natural forest accounted for 60%and that of artificial forest accounted for 55%.About 45%were>2 mm aggregates in 0~10 cm soil layer in natural forest and 23%in artificial forest treated by wet sieve.The proportion of>2 mm aggregates in 0~10 cm soil layer decreased significantly(P<0.05),with a decrease of 58.18%.(2)There were no significant differences in the values of MWD and GMD in the same soil layer of different forest types treated by dry screening(P>0.05).The values of MWD and GMD in wet-screened natural forest were higher than those in artificial forest in all soil layers,and the values of MWD and GMD in this soil layer decreased the most after forest conversion,reaching 45%and 50%,respectively.PAD values of aggregates ranged from 11.07%~30.68%in natural forests.After forest conversion,PAD values in the 0~10 cm soil layer increased significantly by 72.91%(P<0.05).(3)From the perspective of parent rock integration,the results indicated that the MWD value decreased the most in the soil developed by sedimentary rock after forest conversion.It was found that the effects of forest conversion on particle size distribution and stability of aggregates in the whole soil layer were not consistent among different screening methods,which showed that the proportions of particle size of different forest types in the whole soil layer and the variation trends of NWD,GMD and PAD indexes in the soil layer were different under different screening methods.In addition,the structural stability of 0~10 cm topsoil is closely related to soil erosion resistance.Furthermore,the influence of forest conversion on the stability of topsoil aggregates,different aggregates screening methods and differences in parent lithology also affect the stability of top-soil after forest conversion.