Drought Rehydration Of Winter Wheat In Different Drought-resistant Varieties Compensation Effect Study

Winter wheat,as an important food crop,is susceptible to drought stress.It has always been a focus of agricultural research to find out the drought-resistant mechanism of crops and improve their drought-resistant ability and water use efficiency.The effects of repeated drought rehydration during the whole growth period on the physiological growth characteristics and water productivity of different drought-resistant winter wheat varieties need to be further explored,the sensitivity of different physiological indicators to soil moisture is not clear,The physiological mechanism of the occurrence of photosynthetic compensation and growth production compensation needs to be further explored,which can provide a theoretical basis for irrigation strategies to increase crop yield and improve efficiency.In this study,three winter wheat varieties with different drought resistance（Xinong979-S1,Xiaoyan 22-S2 and Wunong 986-S3）were selected,and five irrigation measures of repeated drought-re-watering were set:T1,which was fully supplied with water（75%-85%）during the whole growth period,was used as a control,and two drought levels（mild drought stress（55%-65%）and severe drought stress（45%-55%））of continuous drought and Intermediate re-watering treatment group were set at tillering-jointing stage,where is the field capacity,there were 15 treatments in total.The main results were as follows:（1）The strong drought-resistant variety winter wheat showed stronger physiological drought tolerance under different treatments,and the rehydration treatment group before jointing enhanced the effect of drought exercise,and the physiological indexes of drought tolerance had different sensitivity to soil moisture.The increase range of the activities of superoxide dismutase SOD,peroxidase POD activity and proline Pro,soluble sugar SS,abscisic acid ABA content were shown as Wunong 986>Xiaoyan 22>Xinong 979 during drought treatment.Within 10 days after re-watering under 45-55%water stress,the activities of antioxidant protective enzymes and the contents of osmotic substances in Xinong 979 did not return to adequate water supply level.PCA analysis showed that the score of proline Pro on physiological regulation of wheat was slightly higher,and Pro had high reliability in judging whether the drought level of winter wheat was less than 65%or 55%,and Whether the Pro content was greater than the cutoff value of 13.163μg?g^-1,12.970μg?g^-1,11.690μg?g^-1and 12.24μg?g^-1were used,SOD and SS could only judge whether the drought level was less than 55%。（2）The eties with strong drought resistance were more stable under water regulation and stronger recovery of photosynthetic system after rehydration.The irrigation before jointing improved the drought resistance ability in the later period.photosynthetic indexes had different sensitivity to soil moistureCompared with Xiaoyan 22 and Xinong 979,the net photosynthetic rate（P_n）,transpiration rate（T_r）and stomatal conductance（G_s）of Wunong 986 showed little fluctuation under drought conditions of 45%-55%and 55%-65%,and the recovery of Pn was better after re-watering.G_swas positively correlated with Pn and Tr,and photosynthesis and transpiration were significantly affected by stomatal factors.P_nwas positively correlated with chlorophyll a,chlorophyll b and chlorophyll（a+b）content.The response of chlorophyll a was more significant than that of chlorophyll b,and it tended to decrease or first increase and then decrease under drought stress.Carotenoid content was increased to reduce oxidative damage.P_nwas positively correlated with chlorophyll fluorescence parameters F_v/F_mand q P,and negatively correlated with F_oand NPQ.Chlorophyll fluorescence can be used as an index to judge the influence of drought on photosynthesis.The indexes that were valuable for judging that the soil moisture was less than 65%or 55%are P_n,T_r,G_s,F_v/F_m,q P and NPQ,among which G_shad the highest accuracy for judging that the soil moisture was less than 55%,and the cutoff value of G_swas 0.263 mol H₂O m^-2s^-1.NPQ was the only indicators to identify whether the soil experienced drought before re-watering,and the cutoff values was 2.086 when the soil moisture is less than 55%.（3）The influence of different water treatment on the growth and production of winter wheat was proved,the difference of compensation effect of different drought-resistant varieties and the growth and development characteristics of improved water productivity were clarified,and the optimal irrigation mode was obtained.Drought restricted the growth of plant height,stem diameter and leaf area of winter wheat,and the leaf area was the most negatively affected,and re-watering produced growth compensation.The growth effect of Wunong 986 was better than the other two varieties.The panicle length,thousand kernel weight and yield of the three varieties were higher in the pretreatment group before jointing than in the continuous drought treatment group.Especially under T2 treatment,the yields of Wunong 986,Xiaoyan 22 and Xinong 979increased by 22.73%,10.83%and-2%,and the water use efficiency increased by 22.73%,11.81%and 1.5%.Yield and WUE of winter wheat were positively correlated with panicle length,proportion of effective panicle,thousand kernel weight and leaf area.（4）The correlation degree of the physiology of drought tolerance and Pn in different winter wheat varieties during drought and rehydration periods was analyzed,which clarified the correlation between the compensation of water productivity and drought tolerance physiology and photosynthetic properties of winter wheat.Under drought stress,the POD of Wunong 986 and Xiaoyan 22 and Pro of Xinong 979were the most closely related to P_n.After re-watering,SS of Wunong 986,a strong drought-resistant variety,was more closely related to P_n,and POD of Xiaoyan 22 and Xinong 979 had the highest correlation with P_n,indicating that POD made an important contribution to photosynthetic protection and compensation during the whole process of drought-re-watering.ABA played a more significant role in regulating photosynthesis in weak drought-resistant varieties.The improvement of water productivity was positively correlated with stomatal parameters and chlorophyll content,and the correlation between flowering and filling stage was stronger than that at heading stage.Yield and WUE were positively correlated with F_v/F_mand q P,and negatively correlated with F_oand NPQ.The positive regulation of antioxidant protective enzymes and osmotic adjustment substances provided physiological basis for the normal operation of photosynthetic system and the guarantee of water productivity in winter wheat.