植物降盐效应及其增强土体抗剪强度机理

In this project, Xining Basin and Qaidam Basin (including Qarhan Salt Lake and Da Qaidam Salt Lake), located in the northeast part of the Qinghai-Tibet Plateau have been selected as the test sites. The climate there is arid and semi-arid. The indigenous plants adapted to the local climate and saline soil have been taken as the candidates to study the influence of salt stress at different concentration levels on the plant growth and root strength of these plants. By determining the physiological indexes for these plants and ion content of soluble salt in these plants, the salt-resistance and the salt-absorption capacity for these plants have been assessed. Based on determining the salt content of the rhizosphere soil for these plants as well as the analysis to the variation of salt content in rhizosphere soil and non-rhizosphere soil, the desalinization effect for these plants have been assessed. In further researches, the equation of the 3 components (shear strength for soil, the shear strength due to salt and the additional shear strength provided by the presence of the root) for the root-soil composite system have been established. With the three methods of assessing the shear strength indexes, the analytic solution to shear strength increment provided by roots and the Finite Element Method (FEM) numerical simulation to the root-salt soil composite system subjected to shear loads, the root capacity of increasing the shear strength of the salt soil and the slope stability can be assessed. This study is conductive to control and prevent the salinization of shallow soil, water and soil loss and shallow landslide, meanwhile it has a realistic and theoretical significance in regional environmental and geological protection.

本项研究以青藏高原东北部干旱-半干旱的西宁盆地及其柴达木盆地（察尔汗、大柴旦等1-2处盐湖区）作为研究区，选用适应当地气候和盐渍土条件下生长的乡土植物作为供试种，研究不同浓度盐胁迫条件下对植物生长量和根系强度影响；通过对植物茎叶与根系生理指标、易溶盐离子含量测定，评价植物耐盐性及降盐效应；通过对植物根际土含盐量测定，分析根际土与非根际土含盐量变化，评价不同植物种对土体脱盐效果；建立含盐分根-土复合体抗剪强度的3个组成部分，即脱盐土体的抗剪强度、盐分产生的抗剪强度、根系内聚力产生的附加抗剪强度三者之间相互关系；采用根-土复合体抗剪强度指标评价法、根系增强土体抗剪强度解析解法、根系增强土体抗剪强度有限元数值模拟法，评价根系增强土体抗剪强度及提高边坡稳定性贡献。该项研究对有效防治研究区表层土体盐碱化、水土流失和浅层滑坡等坡面浅层灾害发生，同时对保护区域生态地质环境具有重要理论研究价值和现实意义。

本项研究采用自建种植试验区，野外调查、室内外试验等方法，主要研究内容：（1）试验区建设；（2）植物生长区土体及植物耐盐特征；（3）植物降盐作用及改良盐渍土效应；（4）土体含盐量对抗剪强度影响；（5）植物耐盐与降盐能力及盐含量对根系强度影响；（6）耐盐植物增强土体抗剪强度机理。取得以下重要结果：（1）盐胁迫下老芒麦、垂穗披碱草、柠条锦鸡儿、霸王其株高、地径等生长量指标均表现为逐渐降低。（2）9种盐生植物生长区土体其平均全盐量较未生长区降低3.79 %~85.40 %，且对0~ 20cm深度土体速效磷含量起增加作用。（3）8种盐生植物耐盐性由大至小为白刺、无脉苔草、羊齿天门冬、洽草、赖草、盐地风毛菊、芦苇、海韭菜。（4）含盐量由0.18%增至2.18%，土体黏聚力c值为先增大后减小，其界限阈值为1.18%，内摩擦角φ值逐渐减小。（5）随盐胁迫浓度增高垂穗披碱草、细茎冰草单根抗拉力逐渐减小；单根应力-应变曲线表现为弹性变形、弹塑性变形、应变硬化和断裂破坏4个阶段。（6）垂穗披碱草、细茎冰草和紫花苜蓿，柠条锦鸡儿、霸王和中宁枸杞，其叶片电导率、丙二醛、脯氨酸等6项生理指标均随胁迫浓度增加而增大。（7）随着根系木质素含量增加，盐胁迫后生长期45 d垂穗披碱草、细茎冰草和紫花苜蓿，柠条锦鸡儿、霸王和中宁枸杞其单根抗拉力均呈逐渐增大。（8）含水量和密度为29.01%和1.65g/cm3，5种盐生植物根-土复合体粘聚力c值为10.38kPa-19.19kPa，显著大于素土（5.95kPa），抗剪强度增幅为3.26%～57.18%。（9）重塑垂穗披碱草根系-洗盐素土复合体（含水量12%）含根量分别为0.08%、0.16%、0.24%和0.32%，复合体黏聚力c值平均值为9.39、10.25、12.23、15.36 kPa，其增幅分别为38.50%、51.18%、80.38%和126.55%。（10）7种类型边坡坡面平均位移量由大至小为素土边坡、单一种植边坡、草本+灌木组合种植边坡，位移量减小幅度为71.01%，边坡剪应力集中区截面积减小幅度为71.56%。该项研究对有效防治土体盐碱化、水土流失等灾害发生，对保护区域生态地质环境具有理论研究价值和现实意义。