Diagnosis Of Cucumber Nitrogen And Potassium Stress Based On Microelectrode Technique

Cultivation often happens nutrient imbalance, such as nitrogen(N), potassium (K) stress. The nutrient imbalance will cause apparent changes of plant nutrient content, and there is an interaction between different nutrient elements. So, accurate monitoring and diagnosis of nutrient in crops during the growth process is very important. We can understand quantitatively the nutrient need of crop, establishing accurate nutritional management models. The spectral reflectance of different leaf positions and different sites of cucumber leaves were analyzed. It was used to determine the best leaf positions and sites of cucumber leaves for nitrogen and potassium diagnosis. By analyzing the effect of nitrogen and potassium on morphyological, photosynthesis, fluorescence and electrical parameters,we proposed the early diagnosis method basing the membrane potential,membrane capacitance and light-induced responses of leaf membrane potentials. And we studied the change of membrane potential,membrane capacitance and light induced responses of leaf membrane potentials under different nitrogen and potassium level. The model of bioelectric properties of N or K element was established. Also the model of bioelectric properties of N and K element together was established.The main contents of this paper are as follows:(1) The nondestructive bioelectric system of detecting the membrane potential,membrane capacitance and light induced responses of leaf membrane potentials was constructed. And the right system parameter was setted. The appropriate glass tube was selected, and we analyed the effect of pull 1, pull 2, heat value and time on electrode to get the ideal electrode tip. The measurement methods and steps of membrane potential,membrane resistance and membrane capacitance were introducted. The bioelectric parametera were optimized. Finally, we choosed membrane potential and membrane capacitance for early diagnosis of crop nutrient.(2) To determine the best leaf positions and sites for nitrogen and potassium diagnosis in cucumber, greenhouse experiments were carried out to study the variation of spectral reflectance of different leaf positions and sites. The sensitive wavelength of nitrogen in cucumber was 550 nm, and the sensitive wavelength of potassium in cucumber was 940nm. The best leaf position in the seedling and flowering stage was the 3rd leaf, and the best leaf position in the resulting stage was the 7th leaf. The best leaf site in the seedling, flowering and resulting stage was the tip of I at the leaf edge. So, the best leaf site for the N and K in the seedling and flowering stage was the the tip of I at the edge of the 3 rd leaf. And The best leaf site for the N and K in the resulting stage was the the tip of I at the edge of the 7th leaf.(3) To determine the appropriate parameter for the early of N and K, the variation of morphyological, photosynthesis, fluorescence and electrical parameters under nitrogen and potassium level was studied,and analying the effect of N and K on the different parameter. The plant height, stem diameter, leaf length and leaf width could not distinguish the different nitrogen and potassium nutrient before the onset of the symptoms. Also the net photo synthetic rate,stomatal conductance, the maximum quantum yield and actual quantum yield could not distinguish the different nitrogen and potassium nutrient. The surface properties of cucumber leaves were analyzed. The location of the microelectrode tip in the leaf was determined.And it think that the appropriate light intensity that induced the membrane potential was 800μmol.m-2.s-1. The appropriate light was blue. The measurement of membrane potential in cucumber leaf could be used for pre-visual detection of K stress 8d before the appearance of visually morphological changes. It showed that the membrane potential measurement may be used as an early diagnosing tool for K-stress in cucumber plants. The research on the changs of membrane capacitance found that it was sensitive to N-deficiency. The measurement of membrane capacitance could be used for pre-visual diagnosis of severe and moderate N deficiency 2d before the appearance of visually morphological changes. The research on the changs of magnitude of leaf membrane potential response to light found that it was sensitive to N-excess. An significant decrease of the magnitude of leaf membrane potential response to light could be observed after 3d of N-excess plants. The measurement of the magnitude of leaf membrane potential response to light could be used for pre-visual diagnosis of N excess at least 9d before the appearance of visually morphological changes. It shows that the microelectrode technique that measures the membrane potential,membrane capacitance and light-induced responses of leaf membrane potential are suitable for early diagnosis of N and K-stress in cucumber plants.(4) The membrane potential distribution of different leaf position and different site on the cucumber leaf was analyzed. The result showed that the membrane potential of different leaf position and different site on the cucumber leaf had significant different. And the distribution of membrane potential, membrane capacitance and light-induced responses of leaf membrane potential of different leaf position and different site under different N or K level was analyzed. The result showed that membrane potential rised with the increase of the application of N under different N treatment. The membrane potential declined with the increase of the application of N under different K treatment. The membrane capacitance rised with the increase of the application of N under different N treatment. When the N application reached a certain level, the membrane capacitance did not increase or increased slightly with the increase of the application of N. The magnitude of leaf membrane potential response to light rised with the increase of the application of N and K under different N and K treatment. When the N and K application reached a certain level, The magnitude of leaf membrane potential response to light declined with the increase of the application of N and K. The relationship between N or K application and membrane potential, membrane capacitance, light-induced responses of leaf membrane potentials was analyzed. The result showed that there was a good correlation between N or K content of leaf and membrane potential,membrane capacitance, light-induced responses of leaf membrane potentials. And the relationship was fitted by the line,exponential or quadratic equation. The N or K diagnosis model was established respectively based on membrane potential, membrane capacitance and light-induced responses of leaf membrane potentials. Compared to Rp and RMSEP of nitrogen or potassium model based membrane potential, membrane capacitance and light-induced responses of leaf membrane potentials,potassium choosed the model based membrane potential,nitrogen choosed the model based membrane capacitance and light-induced responses of leaf membrane potentials. Compared to the single model based membrane capacitance or light-induced responses of leaf membrane potentials,the model was better based membrane capacitance and light-induced responses of leaf membrane potentials.(5) The change of the membrane potential,membrane capacitance and the magnitude of leaf membrane potential response to light of the cucumber leaf under N and K interaction was analyzed. The result showed that the interaction between N and K happened to the membrane potential, membrane capacitance and the magnitude of leaf membrane potential response to light of the cucumber leaf. The relationship between N with K application together and membrane potential, membrane capacitance, light-induced responses of leaf membrane potentials was analyzed.Fillaly, the diagnosis model of N and K interaction was established.The model was modified by weight coefficient matrix and interaction coefficient matrix.By comparion we found that the accuracy of nitrogen model based membrane potential, membrane capacitance, light-induced responses of leaf membrane potentials was better than the model that based membrane capacitance, light-induced responses of leaf membrane potentials. the model based membrane capacitance and light-induced responses of leaf membrane potentials was better than the single model based membrane capacitance or light-induced responses of leaf membrane potentials.