| Wheat-cotton interplanting, as one of the important planting patterns, has been widely used in jianghan plain area. However, the continuous rain occurred frequently, which was the key period of wheat yield formation, so the waterlogged stress caused by excessive rainfall in the later period of wheat growth was the main factor limiting high and stabilized yield in the middle and lower reaches of the Yangtze River. At the same time, during August and September in Jianghan Plain, concomitance of hot and waterlogging disaster occurred frequently, which was the critical period of the cotton yield formation. Concomitance of hot and waterlogging disaster often cause the serious cotton buds and bolls shedding during the blooming period, and cause the yield of cotton reduced seriously. Therefore, waterlogging stress disaster has a severe effect on the development of the cotton-wheat double cropping and high yield cultivation mode. This study analyzed the physiological parameter dynamic changes of wheat when suffering surface waterlogging stress, shallow groundwater, and the stress of concomitance of surface waterlogging and subsurface waterlogging in booting stage and filling stage and analyzed the morphological and physiological parameter dynamic changes of cotton when suffering interaction of waterlogging and high temperature, found out the suitable evaluation indexes indicating sensitively to waterlogged stress. Analyzed the yield reduction in quantity under different forms of waterlogged and in different growth periods, on which the corresponding drainage indices was set up. Using the hyperspectral advantages of high resolution, sensitive response, analyzed the canopy spectral reflectance dynamic changes of wheat and the leaf spectral reflectance dynamic changes of cotton under waterlogged stress and its relationship with the physiological and ecological parameters. This research is not only helpful to the scientific development of the cotton-wheat double cropping and high yield cultivation mode but also provides the theoretical bases for scientific drainage in the cooton field and wheat field in the middle and lower reaches of the Yangtze River. The main contents and results are as follows:1. Waterlogging affects hyperspectral characteristics of wheat or cotton and its relationship with physiological parameter dynamicWhen subsurface waterlogging continued for about 17days (groundwater level Ocm, 20cm), the wheat canopy spectral reflectance in the two absorption valleys formed in the blue-purple wave band and infrared wave band increased and the reflection valley became flat, the reflection peak between the two absorption valleys became steep. The more shallow of buried depth of groundwater and the longer of it continuing, the more rising of reflectivity of the two absorption valleys and the flatter of it. Waterlogging caused the reduction of red absorption and red edge "blue shifts". The longer of duration that crop is under shallow groundwater, the more obvious of "blue shifts". The quadratic regression model is selected to stimulate the relationship between Kr and the Chla, Chlb and Chl(a+b) content of wheat flag leaf under waterlogging stress. The established model can be used as a way to estimate chlorophyll content dynamic of the waterlogging wheat flag leaf. Three feature factors--the position of red edge, the kurtosis of red edge, the skewness of red edge are used as the network input layer to establish BP neural network model to estimate the Chla、 Chlb、 Chl(a+b) content of wheat under waterlogging, and the decisive coefficients are 0.8425,0.7002 and 0.8508.After waterlogging occurred during flowering and boll forming stage, the reflection peak in green light wave band became steep, while the near infrared spectral reflectance increased. The more serious of waterlogging and the longer of it continuing, the steeper of reflection peak and the higher reflectance in the near infrared short-wavelength. The waterlogging cotton leaves have obvious "unimodal" phenomenon when the first derivative spectrum ranges from 680nm to 760nm. With the days of waterlogging longer,680-710nm first derivative spectra became high, while 710-760nm first derivative spectra became low. Waterlogging in blooming period caused the reduction of red absorption and red edge "blue shifts". The red edge position drifts towards short wave with 4-5nm on the ninth day. Waterlogging during flowering and boll forming stage enlarge the area of red edge which reach the maximum (0.4842-0.4893) on the sixth waterlogging day. If waterlogging stress occurred continuously after the sixth day, the area of red edge (0.4592-0.4747 on the ninth day) shows a clear downward trend. In this study using the red edge parameter related to the physiological characters of cotton as independent variable, the model is gained in the help of the method of stepwise regression to estimate the physiological characters. The established model can be used as a way to estimate physiological parameter of the waterlogging cotton leaf. Three feature factors---the position of red edge, the kurtosis of red edge, the skewness of red edge are used as the network input layer to establish BP neural network model to estimate the SPAD, Pn, Gs, Ci, Tr, Fv/Fo, Fv/Fm, F PS Ⅱ, ETR, qP and NPQ value of cotton during flowering and boll forming stage, and the decisive coefficients are 0.984,0.985,0.951,0.929,0.983,0.958,0.977,0.959,0.967,0.919 and 0.964.2. Responses of winter wheat to different forms of waterlogged stress and drainage indexWinter wheat suffering from waterlogging in the booting and filling stages resulted in the activity of CAT contained in wheat flag leaf, root system and young panicle had a variation trend that is increased at first and then decreased, In addition to the activity of CAT in root system in booting stage arrives to the maximum when wheat suffers from subsurface waterlogging for 15 days, all the rest of the parts for 10 days,the activity of CAT in young panicle goes up continuously with the increase of waterlogged stress; the activity of POD increase continuously except in young panicle in booting stage and in root system in filling stage, moreover, the heavier waterlogged stress, the stronger amplification of POD activity, the POD activity in young panicle in the booting stage is just the opposite, meanwhile the activity of SOD in flag leaf, root system and young panicle decline with waterlogged stress.When the 0 cm and 20 cm groundwater table sustained 3 d at booting stage and filling stage of winter wheat, the MDA content in flag leaf increased significantly, the soluble protein content decreased significantly, and the soluble sugar content increased significantly. When the 0 cm and 20 cm groundwater table sustained 3 d at booting stage, and sustained 7 d at filling stage, the POD activity in flag leaf increased significantly. When the 0 cm groundwater table sustained 3 d and the 20 cm groundwater table sustained 7 d at booting stage and filling stage of winter wheat, the SOD activity in flag leaf decreased significantly. When the 0 cm groundwater table sustained 9 d at booting stage and filling stage, the Pn, Gs, Ci and Tr decreased significantly, when the 20 cm groundwater table sustained 9 d at booting stage, only the Gs decreased significantly, the Pn, Ci and Tr reduced significantly until last 15 d, when the 20 cm groundwater table sustained 9 d at filling stage, the Pn, Gs, and Tr decreased significantly, the Ci reduced significantly until last 15 d. When the 0 cm groundwater table sustained about 15 d at booting stage and about 10 d at filling stage, the Fv/Fm, F PS II, qP and ETR decreased significantly, and the NPQ increased significantly.wheat suffering from waterlogged damage caused a severe reduction in wheat yield, its yield reduction per plant is 18.4%,45.5%,63.9% and 85.5% in booting stage, and 7.6%,17.8%,43.7% and 70.2% in filling stage as wheat suffer from subsurface waterlogging disaster respectively for 5 d,10 d,15 d and 20 d. If the wheat yield decreased by 15%as the drainage waterlogging standard, the waterlogged time can suffer from is 3.6 days and 6.4 days in booting and filling stage, after drained the surface waterlogging, groundwater table should be lowered down below 70 cm from farmland surface within 3 d. When the 0 cm groundwater table sustained 18 d at booting and filling stage, its yield reduction is 44.77%、 67.73%; when the 20 cm groundwater table sustained 18 d at booting and filling stage, its yield reduction is 17.30%,33.69%; when the 40 cm groundwater table sustained 18 d at booting and filling stage, its yield reduction is 10.45%,10.34%; suggested the underground water level was 50 cm at booting stage and filling stage of winter wheat. Wheat suffering from the stress of concomitance of surface waterlogging and subsurface waterlogging caused a severe reduction in wheat yield, the regression indicated that surface waterlogging has more influence than subsurface waterlogging on yield of winter wheat, if the wheat yield decreased by 15% as the drainage waterlogging standard, the comprehensive drainage indicators SFEW50 should take 275.6-283.6cm·d after anthesis3. Effect of interaction of waterlogging and high temperature on morphological and physiological parameters during flowering and boll forming stage and drainage indexIn normal temperature, the Chla, Chl(a+b) content in the fourth leaf from the top decreased significantly with a minimum of 6 d waterlogging, while in high temperature, the Chla content decreased significantly with a minimum of 3d waterlogging, and the Chl(a+b) content decreased significantly with a minimum of 6dwaterlogging. The influence of waterlogging on Chlb content was not significant, while the Chlb content increased significantly with a minimum of 3d high temperature. In normal temperature or high temperature, the MDA content increased significantly with a minimum of 3d waterlogging, and the influence of waterlogging or interaction of waterlogging and high temperature on MDA content was not significant. The POD activity increased significantly with a minimum of 3d waterlogging or with a minimum of 9d high temperature. In normal temperature or high temperature, the waterlogged stress make the SOD activity decreased and the effect became significant when waterlogged 9d, make the soluble protein content reduced and the soluble sugar content increased, and when waterlogged 3d the effect became significant. With the data in this research, it was concluded that soluble sugar content, POD activity and shedding rates of buds and bolls per plant could be used as key indexes in evaluating and monitoring the stress degree on waterlogging.Waterlogging during flowering and boll forming stages, the component percentage of bolls per plant by August 15 changed non-significantly, but the component percentage of small bolls and buds per plant decreased significantly (except the waterlogging 3d treatment), the number of shedding buds and bolls per plant increased significantly. On September 15, the total number of peach reduced significantly, the numbers of cotton opening peach and green peach reduced significantly when suffered from the lighter waterlogging (the waterlogged days less than 6 d) stress, heavy waterlogging (the waterlogged 9 d and above) stress made the cotton peaches open in advance, the number of early opening peach increase, led to severe premature senescence of cotton. Cotton suffering from waterlogged, hot damage and interaction during flowering and boll forming stage caused a severe yield reduction, the order of influence degree as follows; interaction of waterlogging and high temperature> waterlogging> high temperature. Whether the high temperature condition or normal temperature, the seed cotton yield was significantly lower than control when cotton suffered from 3 d waterlogging. If the seed cotton yield decreasing by 20% as the drainage waterlogging standard, supposing that 4d high temperature in a row appear in the process of waterlogging, the waterlogged time can suffer from is 3.4 days in flowering and boll-forming stage, after drained the surface waterlogging, groundwater table should be lowered down below 80 cm from farmland surface within.3 d. |
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