Physiological And Biochemical Parameters Responses Of Summer Maize To Continous Water Stress And Their Remote Sensing Monitoring

World food security,macro-economic policies,drought and flood monitoring and other key areas affecting global economic development are in urgent need of fast and accurate data support nowadays.And the techonology of remote sensing can fulfill this need.It can offer a efficient and undamaged monitoring on the response of crop to drought,flood and other extreme disasters.However,many researches focus on the analysis of physiological mechanism and productive process,when crops were under drought or waterlogging conditions only.Nevertheless,the dynamic response of summer maize and the sensitivity of physical and chemical parameters to reflectance in different levels under continuous water level from drought to waterlogged are still uncertain which shows a potential knowledge gap.Moreover,these cause the huge difficulty in accurate monitoring the physical and chemical parameters.Based on five years filed data of continuous water stress on maize,this research analyzed the response of maize on continuous water stress.In this study,the phenological period,plant height,leaves areas,fresh and dry weight of roots,stens,leaves and fruits were measured.And the canopy temperature,photosynthetic parameters,leaf water potential,leaf and canopy reflectance were also measured.The yield related indicators were measured when matured.The physiological mechanism of maize under continuous water stress was deeply investigated according to the above data.The reflectance characteristics in different growth periods of in both leaf level and canopy level were revealed.Prospect model and PROSAIL model were employed to investigate the scale effect of reflectance characteristics and vegetation indices.The optimized vegetation indices for different physiological and biochemical parameters were build.Then,the inversion models of different physiological and biochemical parameters in leaf level and canopy level were build and verified.This research further provides reasonable and effective theoretical basis for precise agriculture.The results showed:(1)The plant height,leaf area,ear length,ear diameter,gain weight per plant,ratio of bald tip and ear length,100-kernel weight and theoretical yield of maize all affected by drought stress and the waterlogged stress to some extent.The single leaf area showed the following trend upper>middle>lower in ST1 and ST2.The upper leaf area showed a tendency of increase then decrease from ST1 to ST2 then to ST3.(2)The photosynthetic rate,stomata conduct,transpiration rate and CWSI showed "Twin Peaks" in diurnal variation,while the intercellular carbon dioxide concentration showed "W"form.The photosynthetic rate,stomata conduct,transpiration rate and intercellular carbon dioxide concentration all affected by drought stress and the waterlogged stress to some extent.As the stress was intensified,LWP,LWC,Chlorophyll content and LAI decreased.(3)The absorb depth and area in 1450nm and the reflectance in the near-infrared zone showed the effect of different stresses.The difference a ong different treatments reduced since ST2.In leaf level,NDVI was the most sensitive to LWC,TVI was the most sensitive to LAI,while PRI showed more sensitivity to LWP.In canopy level,NDVI was the most sensitive to Chlorophyll content,TVI was the most sensitive to LAI,while PRI also showed more sensitivity to LAI.No indices were able to capture the characteristics of CWSI in our case.(4)The reflectance of all treatment in the visible spectrum decreased but increased in near-infrared spectrum when LAI increased.The reluctance turned to saturated when LAI increased to 5.The reluctance difiference caused by LAI variation enlarged as the stress of drought was intensified in the short-wave infrared spectrum.The reflectance in near-infrared spectrum was susceptible to LAD variation and changed significantly especially in the closed canopy.The reflectance in short wave infrared spectrum decreased when LAD increased.While it was more susceptible to LAD variation in the closed canopy.The DVI and NDVI increased witibh LAI.DVI decreased with LAD,and was larger in the closed canopy.NDVI was not susceptible to LAD.(5)The optimized indices for different physiological and biochemical parameters in leaf level and canopy level were established.In leaf level,the evaluation model for LWP,Chlorophyll content and LWC.While in canopy level,the evaluation model for LWP,Chlorophyll content,LAI and LWC was build.All models passed the accuracy test.