植被恢复初期的多重固土机制——以重庆缙云山地区2种植物为例

Multiple soil reinforcement mechanisms during the initial phase of vegetation restoration:A case study of two plant species in Jinyun Mountain area of Chongqing

植物措施是水土保持措施的重要组成部分。植物被认为可以多角度加固土壤与边坡。以重庆缙云山地区的乔木种(四川山矾)和草本(狗牙根)作为研究对象,选择一片林窗裸地种植2种植物样本,对种植后3年的土壤抗剪强度、根系分布密度和根系强度等指标进行测定,评估不同植物种在不同种植时期、不同土层的固土效应,探讨不同植物种的土壤加固效应和作用机制,为以固土为主要指标的水土保持植物措施的植物选择提供理论依据。结果表明:1)2个物种都可以通过机械与化学固土作用加固土壤,其中机械加固作用为5~15 kPa,化学加固作用为0~7 kPa。狗牙根仅在种植的第2年,通过其较快生长的特性,在0~20 cm土层提供的土壤黏聚力增加值高于乔木12%,第3年后则高于乔木7%;2)2个植物种对土壤的加固效果都是机械加固作用高于化学加固作用,在0~20 cm土层,狗牙根的机械加固作用比化学加固作用约高52%,而四川山矾则高出26.2%。在20~40 cm土层,四川山矾的机械加固作用高于化学加固作用42.45%,狗牙根则不存在显著差别。不同类型的植物可能通过不同的方式加固土壤,有些可能有较多且强度较高的根系通过机械作用加固土壤;有些可能通过改变土壤本身的有效黏聚力和内摩擦角,通过化学作用加固土壤。寻找不同植物固土能力的特点,可为不同地区固土树种的选择提供理论依据。

[Background]Plant is widely used in protecting soil and water from erosion and shallow landslide,is regarded as an important role in soil and water conservation measures.Plant roots can affect soil cohesion in two ways:Mechanical(root physically penetrate into the soil)and chemical(change the chemical composition of the soil)reinforcement.This study investigated and compared two benefits of plant roots working on soil cohesion with different species restoration in the initial period.[Methods]We selected tree(Symplocos setchuensis)and herb(Cynodon dactylon)as the research object and replanted them in a forest gap for 3 years in Jinyun of Chongqing.Soil shear strength,root distribution density,and root strength traits were evaluated,the benefits of vegetation restoration on soil were measured in different planting period and different soil layer.The chemical reinforcement was measured by direct shear tests,and mechanical reinforcement was measured using RBMw.[Results]1)Both species strengthened soil through mechanical and chemical soil stabilization mechanisms,the mechanical reinforcement ranged from 5 to 15 kPa and chemical reinforcement ranged from 0 to 7 kPa.Both of these two effects decreased with soil depth.2)The C.dactylonis only provided a higher increase in soil cohesion in the 0-20 cm soil layer than the tree by 12%in the second year of planting,due to its faster growth characteristic.After the third year,the increase in soil cohesion provided by the C.dactylonis was higher than the tree by 7%.2)Both plant species demonstrated a higher effect of mechanical soil stabilization over chemical soil stabilization,with the mechanical effect of C.dactylonis being approximately 52%higher than the chemical effect,while S.setchuensis was 34%.[Conclusions]Compared with chemical reinforcement of root,root mechanical reinforcement plays a more important role on soil cohesion,but they varied with different soil layer and different species.More details,different species reinforced the soil via vary mechanisms,some had strong and high-density roots,that provided a higher mechanical reinforcement;while others affected the soil cohesion and internal friction angle via remold and change soil structure,soil organic carbon,and etc.,that provided a higher chemical reinforcement.Thus,this study expands our acknowledge on the mechanism of vegetation works on soil reinforcement and helps us on plant selection for soil conservation.