水蚀风蚀交错带植被恢复对土壤物理性质的影响

Impacts of vegetation recovery on soil physical properties in the cross area of wind-water erosion

黄土高原北部晋陕蒙接壤区是典型的水蚀风蚀交错带和强烈侵蚀中心,探讨该区植被恢复对土壤性质的影响有助于该区植被恢复模式的合理选择和土壤生态效应的科学评价。以神木六道沟小流域为研究区域,探讨了土壤物理性质变化与植被恢复的关系。结果表明,研究区土壤容重、砂粒含量以及饱和导水率普遍较高,表层(0-20cm)均值依次为1.38gcm-3、44.2%和1.46mmmin-1,而土壤总孔隙度与粘粒含量则较低,表层均值分别为45.6%和2.4%,反映了研究区土壤荒漠化的严峻现状,其中北坡(迎风坡)表现尤为严重。与农田相比,采用自然弃耕、种植紫花苜蓿(Medicagosativa)和柠条(Caragana korshinskii)、恢复次生天然草地等不同的植被恢复模式可以不同程度地降低土壤容重,增加土壤总孔隙度、饱和导水率以及团聚体稳定性,改善土壤的物理性质,而且随着恢复时间(1-30a)的延长,这种效应会进一步增强。通过种植人工草地并使其自然恢复为次生天然草地的植被恢复模式,对土壤结构的改善作用显著优于直接种植柠条灌丛和自然弃耕等模式。但是,短期内(<30a)植被恢复对土壤颗粒组成、比重等物理性状无显著影响,意味着土壤一旦出现沙化将很难逆转。从对植被恢复响应的敏感性而言,土壤容重、总孔隙度以及团聚体稳定性可以作为土壤生态效应评价的主要指标。

The border area of Shanxi,Shaanxi,and Inner Mongolia provinces is a typical cross area of wind-water erosion and the severe erosion center in the north of the Loess Plateau of China.Investigation of the impacts of vegetation recovery on soil properties is important for the reasonable selection of vegetation recovery models and assessment for ecological effects.The relationship between the changes in soil physical properties and vegetation rehabilitation was studied in Liudaogou catchment located in Shenmu County of Shaanxi.The results showed that soil bulk density （ BD） ,sand content, and saturated conductivity （ Ks） of surface soil （ 0-20 cm） were commonly high with average values of 1.38 g cm-3, 44.2% ,and 1.46 mm min-1,respectively,while soil total porosity （ Pt） and clay content were low with average values of 45.6% and 2.4% ,indicating the serious status of soil desertification.Soil degradation in the north windward slope was more severe than that in the south leeward slope.Compared with farmland,vegetation recovery and restoration,including farmland abandonment,planting Medicago sativa and Caragana korshinskii,and natural grassland restoration could significantly ameliorate soil physical properties through reducing BD and increasing Pt,Ks and aggregate stability.Moreover,these effects would be enhanced during the process of vegetation restoration from 1 to 30 a.Compared with farmland abandonment and planting shrub,secondary natural grassland restoration through establishing artificial grassland might be the best pattern in ameliorating soil structure.However,the impacts of vegetation recovery on soil mechanical composition and density were not significant in a short period （30 a） ,implying that the degrading situation is hard to be reversed after desertification occurred.As respect to the sensitivities in responding to vegetation recovery,BD,Pt,and aggregate stability could be the major indexes for soil ecological assessment.