| Crop water status affects the changes of physiological and biochemical indexes of crops.Accurate acquisition of crop water status helps to timely irrigation,precise irrigation and improve irrigation efficiency.Hyperspectral technology has the advantages of fast,nondestructive,no pretreatment and low cost,which is widely used in crop monitoring.In this study,a pot experiment of maize was conducted under artificial simulated high temperature and drought stress conditions to study the relationship between canopy reflectance spectrum and plant water content and leaf water content under different temperatures and irrigation amounts.The effects of high temperature and drought on photosynthetic characteristics,chlorophyll content,antioxidant protective enzyme activity,dry matter quality,plant height,root morphology and other indicators of maize were analyzed.The correlation between plant water content,leaf water content and canopy spectrum was explored to determine the sensitive band of water status,and the model of water index and spectral sensitive band was established to provide a basis for real-time non-destructive monitoring of water status of maize plants and stress-resistant cultivation management of maize.The main conclusions are as follows:(1)After single-factor high temperature stress and dual high temperature and drought stress at jointing stage,compared with normal temperature and suitable water treatment,the net photosynthetic rates of high temperature and suitable water treatment,high temperature and severe drought stress treatments were significantly decreased by 39.78%and 57.13%,and SPAD values were decreased by 34.99%and43.19%,respectively.Irrigation should be sufficient during high temperature stress to prevent the superposition of high temperature and drought and reduce the adverse effects on maize.(2)The grain weight and 100-grain weight of maize under normal temperature and suitable water treatment were the largest,which were 53.85 g and 24.37 g,respectively.However,the harvest index of normal temperature and mild drought treatment was the largest,which was 0.33,indicating that mild water stress at normal temperature can promote the transfer of photosynthetic products to grains.High temperature and drought stress at jointing stage could lead to the decrease of maize yield,and the decrease rate increased with the increase of stress degree.(3)The high temperature and drought stress at jointing stage of maize increased the activity of antioxidant protective enzymes in leaves to varying degrees.With the increase of stress duration,MDA content significantly accumulated.Peroxidase activity increased with the increase of high temperature and drought stress,but catalase activity increased first and then decreased with the increase of drought stress.At the same time,catalase activity decreased with the increase of temperature.After rewatering,the peroxidase activity increased significantly,and the catalase activity and MDA content decreased to room temperature and suitable water treatment.(4)High temperature treatment significantly reduced maize root length,root volume,root surface area and root average diameter.Although the occurrence of drought at jointing stage had no significant influence on maize root length,root volume and root surface area,it would lead to the decrease of maize root diameter.At tasseling stage,the root length and root volume of maize under normal temperature×mild drought treatment were the largest,which were 18357.4 mm/plant and 24.79cm~3/plant,respectively.The root surface area under normal temperature×suitable water treatment was the largest,which was 1914.77 cm~2/plant.Under high temperature conditions,the root length,root volume and root surface area of maize increased significantly after re-watering treatment,but the maximum values were significantly lower than those under normal temperature conditions,indicating that although the root growth of maize after re-watering showed a compensation effect,it was unable to restore to the normal level,and the damage of high temperature and drought on maize root had been generated.(5)The variation trends of canopy reflectance of maize under high temperature,drought and high temperature and drought stress were consistent,but the reflectance values of different bands under different treatments were different.In the range of 400-670 nm,the spectral reflectance under the same temperature and different water treatments was different,but the difference was small.The spectral reflectance under severe drought stress was the highest,and the spectral reflectance under suitable water treatment was the lowest.In the 770-1350 nm band,the spectral reflectance of different irrigation treatments was significantly different.The spectral reflectance of suitable water treatment was the highest,and the spectral reflectance of severe drought stress was the lowest.In the range of 1451-1800 nm,the reflectivity increases with the increase of water stress.(6)The moisture content of maize plants and leaves at jointing stage was negatively correlated with 350-670 nm band reflectance,and positively correlated with 770-1350 nm band reflectance.Under different water treatments,the correlation between the water content of maize plant and leaf and the original band reflectance and vegetation index was different.With the increase of irrigation amount,the correlation between the water content of maize plant and leaf at jointing stage and the original band reflectance and vegetation index was greater.The correlations between plant water content and leaf water content with original band reflectance and vegetation index were also different.On the whole,the correlations between leaf water content and original band reflectance and vegetation index were greater than plant water content.(7)According to the analysis of the correlation between maize moisture content and vegetation index,the vegetation index that was sensitive to maize moisture content under different water treatments was selected.The vegetation index selected by each water treatment was gradually linear regression.The determination coefficient R~2of the regression equation suitable for water treatment was higher than that of mild drought treatment and mild drought treatment.The R~2of the regression equation of plant water content and leaf water content were 0.74 and 0.88,respectively.The accuracy of regression model established by maize plant moisture content and leaf moisture content was different.Compared with R~2of maize plant moisture content regression equation,R~2of leaf moisture content regression equation increased 7.04%-20.37%. |
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