Research On Water Transporting Mechanism In Plant And Method Of Judging Crop Water Deficit In Greenhouse

Water shortage is one of the most serious problems in the world. As an agricultural and populous country, China is facing the crisis of lacking water. Water-saving is not only the requirement of our national economy and sustainable development, but also the effective measure of solving water shortage and unbalance of water distribution. Water saving depends on strengthening the study on the technology in this field and developing high efficient water-saving agriculture. Biological technique has become an effective way in solving agricultural drought, which can reduce the extravagant transpiration of crop by well-timed irrigating base on plant water requiring. This work is supported by the Doctoral Program Foundation of State Education Ministry of China "The research on information of water requirement and controlling system of water saving irrigation in greenhouse"(No.20010183016) and Natural Science Foundation of Jilin Province "Research on controlling mechanism of water saving environment in greenhouse"(No. 20020657). Based on the theory of energy balance and water balance in the SPAC (Soil-Plant-Atmosphere Continuum), this paper refers to water transporting mechanism in plant and method of detecting crop water stress in the greenhouse according to plant information as follows: 1) Based on the equation of steady and unsteady water transporting in plant, the paper discussed that the effect of water potential, water resistance and water capacity on the transferring of water in SPAC. According to the change of liquid transportation and transpiration, analytical equation of water potential was formed based on the transpiration. The experiment showed that the velocity of stem sap flow lagged the changing of transpiration; the water potential and capacitance regulate the equilibrium between the liquid transporting and transpiration in plant. 2) Under different water status of plant, the paper studied the changing characters of water potential(ψ), water resistance(R) and water capacitance(C). The leaf potential had the descending threshold followed by soil moisture going down, but the leaf water potential also be influenced by the meteorological factors such as air temperature, humidity and solar radiation. therefore, when the leaf potential is taken as the CWSI (Crop Water Stress Index), the influence of environmental factors should be take into account in order to ensure the accuracy of detecting water deficit of plant. Based on the experiment about plant transpiration, controlling the meteorological factors, such as solar radiation and VPD, can improve the WUE (Water Use Efficiency); 3) Based on the energy balance of SPAC, the paper concluded the relation between leaf-air temperature differences and environmental factors, and made a path analysis about air temperature, VPD (Vapor pressure deficit), PAR (photons flux). The result showed that the leaf temperature was affected directly by the air temperature and indirectly by VPD and PAR, the leaf-air temperature difference linearly correlated with VPD and PAR, therefore, solar radiation and wind must be considered in the application of CWSI with the Idso empirical model. 4) The leaf temperature is affected by both environmental and plant interior factors, thus leading to the uncertainty of application in detecting the crop water status with CWSI. The paper discussed the calculation of CWSI with fuzzy-Neural logic method in detecting crop water deficit. The input includes leaf-air temperature difference, VPD, solar radiation and wind, and the output is CWSI. Compared with the traditional model such as the Idso empirical model and the Jackon theoretical model, the experimental result with fuzzy-Neural logic method can effectively reflect the water status of crop, without appearing the phenomena of "CWSI>1". 5) External stimuli (e.g. changing air-temperature and moisture, water availability, wounding or mechanical stimulation) causes an action potential (AP) to be generated and changes the variation potential (VP) from the original state level. Based on the character of plant electrical signals, the paper introduced the technology in developing the measuring system of plant electrical potentials, the input impedance of the amplifier must be high enough (≥1010-1012Ω) for measuring the plant weak signals, ensuring...