Effects Of Shading And Waterlogging Stress At Jointing Stage And Hyperspectral Response Of Summer Maize

In order to improve the disaster prevention and mitigation ability of summer maize in the Anhui province,Jiangyu 877 summer maize was used as the research object in this study.The characteristics of various physiological indexes and hyperspectral reflectance of summer maize after 3,5,7,and 9 days of shading and waterlogging at the jointing stage were analyzed.Then the estimation model of maize leaf SPAD,relative electrical conductivity and soluble sugar content were constructed by hyperspectral technology.The main results are as follows:(1)Compared with the control group,the plant height of summer maize in the experimental group decreased by 4.11%,3.47%,15.53%and 1.56%respectively,indicating that the compound stress for 7 days had the most serious effect on the plant height.After 3days of shading and waterlogging,the fresh weight of the experimental group was 5.47%higher than that of the control group.It indicated that short-time shading and waterlogging stress would enhance the water absorption of plants.Compared with the control group,the dry weight of maize plants in the experimental group decreased by 23.06%,26.21%,28.77%and 33.87%,indicating that the longer the duration of stress,the deeper the impact on the formation and accumulation of dry matter in summer maize.(2)The SPAD value of summer maize leaves under stress was significantly reduced16.60%compared with the control,indicating that the coupling stress of low light and waterlogging at jointing stage broke the normal growth and development process of summer maize at jointing stage,and reduced the chlorophyll content of leaves.The coupling stress of shading and waterlogging at jointing stage increased the relative electrical conductivity of summer maize leaves.The experimental group was 16.82%,13.29%,57.34%and 94.37%larger than the control group,respectively,and showed an overall trend of increasing with the extension of stress time.It indicated that the longer the stress time,the deeper the damage to leaf cells.The content of soluble sugar in the leaves of the experimental group was 8.71%more than that of the control group,and it showed a slight increasing trend with the growth of stress time.For POD,the experimental group increased by 15.15%,3.98%,60.73%and79.91%,respectively,compared with the control group,showing a significant upward trend in general.It showed that with the increase of stress time,the stress resistance of summer maize leaves became stronger.(3)Compared with the control group,the total proportion of unhealthy pollen increased by 41.04%,67.48%,118.99%and 145.29%under low light and waterlogging.The proportion of unhealthy pollen doubled.Furthermore,stress also resulted in smaller oval pollen grains.The results showed that shading and waterlogging stress at jointing stage had significant effect on pollen vigor and shape.In addition,the grain quality of summer maize under low light and waterlogging stress at jointing stage decreased.Compared with CK,the long axis of summer maize pollen grains in the experimental group decreased by 3.62%,10.6%,14.15%and 14.92%,respectively.And the short axis decreased by 4.10%,11.73%,11.63%and 14.60%,respectively.Compared with CK group,the protein content of summer maize grains in experimental group decreased by 1.26%,6.35%,9.69%and 12.15%,respectively.Starch content decreased by 1.30%,3.09%,4.23%and 4.81%,respectively.And fat content decreased by 2.99%,10.69%,12.74%and 13.77%,respectively.Besides,crude fiber content decreased by 4.94%,7.34%,7.51%and 7.89%,respectively.The results showed that the longer the stress duration,the lower the grain quality of summer maize.(4)With the duration of stress,the"green peak"of hyperspectral reflectance curve of control leaves was always higher than that of experimental group,indicating that stress reduced the chlorophyll content of summer maize leaves.The"red valley"characteristic curve changed from coincidence to control higher than experimental group.As for the feature of"near-infrared platform with strong reflection",it first strengthens and then weakens.Compared with the control,it changed from higher in the experimental group to lower in the experimental group after 7 days of low light and waterlogging,indicating that chlorophyll was the most sensitive to the combined stress of low light waterlogging.(5)The estimation models for SPAD,relative electrical conductivity and soluble sugar of summer maize leaves under weak light and waterlogging stress were using hyperspectral reflectance combined with machine learning algorithm.The correlation between SPAD and hyperspectral reflectance is the most significant.And the estimation model of SPAD is the most precise.The SPAD value estimation model of summer maize leaves under shading and waterlogging stress constructed by the negative correlation characteristic band of the first derivative spectra combined with the RF algorithm has the best effect.The R~2 of training set reaches 0.945,and the RMSE is 1.567.Besides the R~2 of testing set is 0.913,and the RMSE is 1.010.The relative electrical conductivity estimation model constructed by positive correlation characteristic band of the first-order derivative spectra with BPNN was best.The R~2 of training set reaches 0.875,and the RMSE is 2.179.Besides the R~2 of testing set is0.854,and the RMSE is 1.698.The soluble sugar estimation model constructed by negative correlation characteristic band of the first-order derivative spectra with GRNN was best.The R~2 of training set reaches 0.759,and the RMSE is 1.911.Besides the R~2 of testing set is 0.759,and the RMSE is 2.375.