Study On Sensing Mechanism And In-situ Detection Of Plant Water Relations

Plant water relations are very important branch of plant physiology.It studies the absorption of water by plants,the water transport in plants,and loss to the atmosphere(transpiration),and the response and adapt to plant to water stress.The effective plant water physiological information is not only the production guidance information urgently needed by the agricultural and forest producers and ecological maintenance personnel,but also the research subjected that the plant physiologist has focused on for long time.In this dissertation,the sensing technology based on the dielectric theory and the innovative experimental methods that embedded micro sensors into small plant were used to obtain information on plant water physiology.The experiments were carried out in combination with potted sunflower,potted apple tree,apricot and cheery-apples trees in orchard.The study was completed under the funding of the National Natural Science Foundation of China(NSFC)and the German Science Foundation(DFG)(project number:GZ1272).In this paper,a systematic and theoretical analysis and experimental study of the plant water physiology information sensing mechanism and in situ detection method are carried out in the following aspects:(1)Based on the physiology structure of the woody plant stem,analyze the design requirements of stem water sensor which will be applied to woody plant stem water detection.According to the design requirements of the undamaged in-situ measurement,an annular elastic electrode design with the inner fringe field is proposed.Combined with the theory of dielectric physics,the volumetric water content of plant stems was mapped to the load impedance composed of plant stem and electrodes,and the principle of port impedance measurement was analyzed from the perspective of the transmission line theory.A network analyzer was used to analyze the frequency of the load impedance formed by the electrodes and stems.The selected measurement frequency was 100 MHz.The design of the impedance detection circuit was given.(2)To test the feasibility and performance parameters of the designed high-frequency inner-edge field capacitance sensor,a series of evaluation tests were conducted in the laboratory.Using experimental testing,simulation software analysis,and anatomical observation,determined the effective sensing depth(ESD)and allowable maximum stem diameter(AMStD)with woody plant stem.Make clear the relationship between the stem diameter and the sensor sensitivity,and the effect of temperature on the measurement,and the calibration equations for various diameters are given.(3)The stem water sensor was applied to potted apple trees in a greenhouse.Based on the relative changes in stem water recorded by the sensor,the daily variation of water in apple stems was analyzed.Under the condition of controlling the water supply of apple trees,the sensor observed the water deficit stresses response and response recovery of the stems.In the orchard environment,the on-line quantitative monitoring of the stem water with different diameters on the same apricot tree verified the expansion of the maximum allowable diameter of the measured diameter with the temperature correction.At the same time,the hysteresis loops of different height stem were also observed.In the long-term monitoring of stem water in the orchard environment,the seasonal variation in water content of the stems of the cheery-apple trees was observed,and the long-term stability of the sensor was also verified with this test.The application of this sensor in the study of cold acclimation and warm de-acclimation of woody plants is also seen.In addition,the sensor was also used in the monitoring of stem rot with chreey-apple tree,providing a method of the diagnosis and monitoring of dry rot disease in the Rosaceae species from the viewpoint of stem water detection.(4)Finally,this study proposes an innovative test method of small plants that use micro body grafting technology to embed miniature passive sensors in small plants to observe physiological information.In this study,grafting technology was used to implant micro thermocouple sensor arrays in the middle of two sunflowers growing in the same pot.Cold water irrigation tests were designed to observe the response of sunflower samples during irrigation events.When the temperature of the irrigation water is lower than the temperature of the test plant,the upward flow of the stem fluid induces a temperature gradient along the axis of the stem.Therefore,an array of implanted thermocouple sensors can be used to track the hydrothermal response to sunflower samples and to analyze the root and stem water conductance of the plants.The results observed in this experiment are secondary,and the micro passive sensor embedding method provides inspiration for physiological information acquisition of small plants with more micro sensors in the future.