基于内边缘场电容效应的树干/枝水分传感器研究

茎秆水分与茎流速率是解析植物茎秆内水分传输的2个重要参数。设计了一种基于内边缘场电容效应的树干/枝水分传感器。采用有机溶液试剂法与枝条冻融法分别对传感器做了性能测试试验,证实了传感器在相对介电常数16.8~81变化范围内具有很好的线性关系(R2=0.977 2),并从冻融-干湿等价性能看,传感器反应灵敏度满足测量要求。利用枝条脱水法得到了传感器参考标定曲线,决定系数为0.992 2。温室环境下的盆栽苹果树试验证实了该传感器既可无损观测树干细胞昼夜间的充放水过程,还可感测亏水树干内膨压崩溃与恢复过程。

Inner Fringing-field Capacitance Sensor for Measurement of Stem Water Content

Stem water content and sap flow rate are regarded as two important parameters associated with water transport through plant stem. Gamma-ray instruments, although often highly accurate and noninvasive, carried a potential risk of radiation exposure restricting their applications. The MRI method is noninvasive and safe, but it is costly and impractical for long-term monitoring of plant water status in natural circumstances. Generally TDR and FD sensors are often regarded as invasive methods because both techniques are depended on inserting two or more waveguide lines into the stem, causing some tissue damages in the stem. For this purpose, a novel sensor was presented based on the inner fringing field of capacitor. The sensor comprises a pair of metallic electrodes designed to wrap around stems likes an upper and a lower strap ring. The strap-rings were connected to a high frequency oscillator operating at 100MHz. Because the dielectric property of stems is closely correlated with the amount of water in the stem, stem water content can be measured without causing stem tissue damage. To verify its technical performance, firstly, three different physical tests were conducted in the laboratory. The results confirmed that both sensitivity and linearity of the sensor were satisfactory. Then these sensors were tested with three potted apple trees grown in a greenhouse. By using the proposed technique, the actual water recharge and discharge occurred between the stem tissues and the water pipes in the stem were successfully observed. Furthermore, the turgor breakdown and recovering process were observed when these apple tree samples suffered from water deficit. In general, all measured data were clearly interpretable to the known knowledge of plant water relation