Evaluation of the root-border-cells function in rhizosphere to decrease soil mechanical impedance.

在紧实土壤中生长的植物根必须克服土壤对根伸长的机械阻抗。根边缘细胞层可以减少土壤与生长根之间的摩擦力。我们试图评估根缘细胞在降低土壤机械阻抗方面的作用。在一系列实验中，我们发现：1.我们首次量化了根边缘细胞在研磨性生长介质中的脱落速率。紧凑型玉米根缘细胞数由1930增加到3220d^-1~(-1)。在压实砂中，整个盖子表面积被脱落的细胞覆盖，而在松散砂中，这一比例约为7%。2.我们开发了一种图像分析程序来量化根冠中段纵切面中的细胞位置。仅有7%的根部最外层的细胞与帽小柱区域相关。3.机械阻抗略微增强了根冠外侧区的分生组织活性。细胞产量紧凑型为2,010个，松散型为1,570个。4.根冠的存在在很大程度上减轻了对根渗透的机械阻抗，并使根在压实土壤中生长得更快。5.根缘细胞对根冠降低土壤阻力的贡献率为58%。6.建立了根缘细胞与土壤颗粒的分离技术。湿润土壤中的根缘细胞数量显著多于干土壤，说明根缘细胞的润滑层降低了土壤渗透的摩擦阻力。

Plant roots grown in compacted soils have to overcome the mechanical impedance of the soil to root elongation. The friction between soil and the growing root may be decreased by the layer of root border cells. We tried to evaluate the role of the root border cells to decreasing the soil mechanical impedance. In the series of experiment, we found the following:1. For the first time, we quantified the rate of sloughing of root border cells in an abrasive growth medium. The number of maize root border cells increased as a result of compaction, from 1930 to 3220 d^<-1> per primary root. The whole of the cap surface area was covered with detached cells in compacted sand, compared with about 7% of the surface area in loose sand. 2. We developed an image analysis procedure to quantify cell locations in the median longitudinal section of root caps. Only 7% of cells in the outermost layer of the root were associated with the columella region of the cap. 3. Mechanical impedance slightly enhanced meristematic activities in the lateral region of the root cap. Cell production rates were 2,010 cells d^<-1> in compact and 1,570 cells d^<-1> in loose. 4. The presence of a root cap alleviates much of the mechanical impedance to root penetration, and enables roots to grow faster in compacted soils. 5. The contribution of root border cells to the reduction in soil resistance by the presence of root cap was 58%. 6. A technique was developed to separate root border cells from soil particles. The number of root border cells in wet soil was significantly greater than that in the dry soil.In conclusion, the lubricating layer of root border cells decreases frictional resistance to soil penetration.