| Because of the intensification of anthropogenic disturbance, global temperature has increased 0.6?averagely in the past one hundred years. Furthermore, it is predicted that the earth will be warmer 1.4?-5.8?by the end of this century. At the same time, the frequency of extreme climate events (such as extremely high temperature in summer) will be higher, and their duration will be longer in many areas in world. Thus, the crop system would be challenged by more frequent high temperature. Rice is one of the most important grain crops in China, which is easily confronted with summer high temperature in its sensitive growth period. In recent years, the heat injury of rice has been intensified in southern China, especially Yangtze-Huaihe region. Therefore, it is very important in China to understand the occurrence law of rice heat injury; explore its mechanisms of rice heat avoidance and resistance and explore estimation methods of rice heat resistance.Occurrence probability, annual mean day, beginning and ending time of high temperature were analyzed respectively with daily average temperature and the highest temperature from agrometeoroloical stations in June and August of 1965 to 2004 in Hunan, Hubei, Jiangxi, Anhui, Jiangsu and Zhejiang provinces. Time-space distribution rule of six provinces were summarized according to the above analysis, and measures of avoiding from high temperature and corresponding strategies were provided. In order to explore eco-physiological mechanisms of rice heat avoidance and resistance and technical methods, provide an important theoretical basis for the selecting rice cultivars of heat resistance and heat mechanism of rice, physiological and biochemical characteristics of flag leaves, pollen vitality, pollen germination ratio, rice yield, rice yield components, rice quality and canopy spectral reflectance indexes of different growth stages in Yangdao 6 and Nanjing 43 were studied in field and room experiments under different high temperature during booting stage. The relationships between canopy spectral reflectance and agronomic parameters of leaves, rice yield, rice yield components and rice quality were analyzed. Canopy spectral reflectance change and specific laws of agronomic parameters, rice yield and rice quality were understood. Regression equation and spectral estimation model of rice growth, yield and quality were established. The results provided important theoretical basis for monitoring rice heat damage by hyper-spectral remote sensing.In conclusion, the main development and results as follows:(1) Time-space distribution of high temperature in middle and lower reaches Yangtze RiverTime-space distribution law of high Temperature in middle and lower reaches Yangtze River in 40 years as follows:Probability of average temperature?30?is greater than that of the highest temperature?35?in plain region; adverse in mountain region. Probability of high temperature is more in the further south and interior region; probability of high temperature in coastal region is lower. Region of more probability in high temperature is corresponding to earlier beginning and late ending under 80% guarantee, vice versa. Region of lower probability in high temperature is corresponding to late beginning and earlier ending under 80% guarantee. Law of high temperature days is the same to probability in high temperature. The average and the highest temperature anomaly has periodic transformation in recent 55 years in Nanjing, that is, pre1970 and post 1990 (1970 to 1990) is high (low) temperature year. High harm temperature weather at rice florescence often occurs in recent 55 years, the frequency of average temperature?30?is obviously more than that of the highest temperature?35?weather, the frequency of both of them have increased since 1990.(2) Change character of physiological and biochemical characteristics, yield and grain quality of rice under high temperature stressCompared with the CK, pollen vitality, pollen germination ratio, seed setting ratio and yield in Yangdao 6 and Nanjing 43 were lower significantly by high temperature stress (p<0.01). With the elevation of stress temperature and extension of stress time, pollen vitality, pollen germination ratio, seed setting ratio and yield of two rice cultivars suffered a sharply decline, the difference of residual three indexes under three high temperature treatments were significant at 1% and 5% levels except yield. But thousand seed weights and panicle number had no obvious changes. According to the correlation analysis, the rate of seed setting and yield of two rice cultivars showed a significantly linear correlation with the rate of pollen vitality and pollen germination ratio (p<0.01),respectively. Therefore, pollen viability and pollen germination rate could be as the indexes of high temperature heat injury. According to the thermal injury index, Yangdao 6 is a cultivar of high temperature resistance, Nanjing 43 is a cultivar of heat sensitive.Compared with the CK, physiological and biochemical characteristics of leaves in Yangdao 6 and Nanjing 43 were lower significantly by high temperature stress (p<0.05). Chlorophyll content, superoxide dismutase (SOD) activity, ascorbic acid (ASA) content, glutathione (GSH) content, proline (Pro) content, soluble protein content, soluble sugar content, net photosynthetic rate (NPn) and leaf area index (LAI) suffered a sharply decline, relative conductivity, malondialdehyde content (MDA) increased gradually, the fomer 9 indexes (the latter 2 indexes) decreased (increased) with the elevation of stress temperature and extension of stress time. The response of Nanjing 43 to high temperature was bigger than that of Yangdao 6. According to the correlation analysis, grain yield showed a positive correlation with NPn at 0.01 level, the correlation coefficients of them were 0.94 and 0.88 respectively. The correlation between grain yield and DW after initial at mature stage, the export percentage of the matter in stem-sheath (EPMSS) and the transformation percentage of the matter in stem-sheath (TPMSS) were not significant. It was showed that grain yield originated mostly from the leave photosynthesis after booting. Six leave physiological and biochemical indexes which were significant correlation with heat injury index were analyzed by stepwise regression. Soluble sugar content and GSH can be used as biochemical indexes to indentify heat resistance of rice.Brown rice rate, milled rice rate and head rice rate in Yangdao 6 and Nanjing 43 were lower, chalkiness rate and chalkiness degree were higher by high temperature stress. With elevation of stress temperature and elongation of stress time, the damage on processing quality and appearance quality in two rice varieties were more serious. Eating quality including soluble sugar content and protein content in two rice varieties were lower, amylose content were higher compared with the CK. Soluble sugar content and protein content (amylose content) rapidly decreased (increased) with the elevation of stress temperature and extension of stress time. Therefore, high temperature stress affected the booting of rice eating quality. The damage degree of processing quality, appearance quality and eating quality for Nanjing 43 was litter higher than that for Yangdao 6 under the same temperature stress. (3) Red edge characteristics and monitoring of SPAD and LAI for rice with high temperature stressSPAD value and LAI of two rice cultivars presented a tendency from rising to falling with development of growth stages, which meant SPAD value and LAI up to peak value on flowering stage and turning lower value on heading and waxy maturing stages. The SPAD value and LAI would decrease with the elevation of stress temperature. There were'red shift' phenomena before flowering and 'blue shift' phenomena after flowering for the red edge position?red, red edge slope D?red and red edge area Sred of canopy spectrum. These three parameters of red edge also presented'blue shift' phenomena with the elevation of stress temperature. The SPAD value and LAI of rice flag leaves at different growth stages were significantly or very significantly correlative to the red edge features variables, Compared to D?red, the model of?red could forecast SPAD value and LAI of rice flag leaves more reliably.(4) Estimation study of rice yield and grain quality with hyper-spectral remotesensing under high temperature stressBy contrast with ripening stage, the correlation among the spectral indexes during flowering and filling stages and theoretical yield, actual yield, panicle number permu, panicle number, kernel weight, panicle length, panicle weight and seed setting was high with significant level of P<0.05, and those stages could be used as a key stage of predicting rice yield. In these spectral indexes, difference vegetation index called as DVI (810, A(450, 560,680)), perpendicular vegetation index called as PVI (810,680), peak value of red edge and area 670-755 could be used for simultaneously estimating the theoretical and actual yield of matured rice. Further, DVI (810,450) and (810,560), PVI (810,680) and peak value of red edge could be used for simultaneously estimating the panicle number permu, panicle number and kernel weight of matured rice.There were significantly or very significantly correlation of grain crude protein content, amylose content and soluble sugar content with canopy spectra and the first derivative at different growth stages in some wave band. The relationships of grain crude protein content, amylose content to the ratio, differential and normalized difference vegetation indices of all bands and red edge parameters were also analyzed. The fitting spectral parameter with better correlation was subsequently selected through regression analysis, DVI (810,450) was found to be the best parameter for predicting grain crude protein content (GCPC), grain amylose content (GAC) and grain soluble sugar content (GSSC) in rice. The estimation precision was 0.39-0.68, estimation accuracy was 0.71-0.92, and RMSE was 8.71%-11.30%, which indicated a good fit between the predicted and observed values of grain crude protein, amylose content and soluble sugar content. |
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