Physiological Response Of Water-saving And Drought-resistant Rice To The Drought-rehydration Process And The Regulation Of Alternate Wet And Dry Irrigation

Rice（Oryza sativa L.）is the most water-intensive food crop in agriculture,global climatechange could worsen water availability when water scarcity threatens rice production and the sustainability of high-yielding irrigated rice ecosystems.The Jianghuai hills are a typical region with high incidence of seasonal drought at the booting stage,which is a bottleneck to high and stable rice production in the region,and can lead to lower rice yields under drought stress at this time.Previous studies have shown that drought stress during the gestation period reduces yield mainly due to photosynthetic limitation.Water-saving and drought-resistant rice（WDR）under drought conditions provides a good physiological basis for high photosynthetic production in rice after rehydration by maintaining a high photosynthetic production potential,and effectively avoiding damage to photosynthetic structures,thus achieving higher yields.As an effective water-saving irrigation method,alternating wet and dry irrigation has a significant impact on the physiology and yield of rice.In this study,three water treatments,conventional flood irrigation（W0）,light alternating wet and dry irrigation（W1）and heavy alternating wet and dry irrigation（W2）,were selected for WDR,Hanyou73（HY73）and the conventional variety Huang Huazhan（HHZ）,and different degrees of drought and rehydration were applied sequentially at the booting stage to study the characteristics of changes in antioxidant enzyme systems,osmoregulatory substances and endogenous hormones during this process and their relationship with yield.On the basis of the effects of drought and rehydration on the photosynthetic production potential of WDR,the effects of different water regimes on the physiological changes of WDR under drought were investigated,as well as their effects on yield and yield components.The main results were as follows:1.WDR and light alternate dry and wet irrigation coupled was the combination model tomaintain yield advantage after extreme drought.After drought and rehydration at the booting stage,the yield,filled grain and thousand grain weight of WDR,HY73 were significantly higher than those of HHZ（P<0.05）;the yield level of the alternating light dry and wet treatment was significantly better than those of the other two treatments（P<0.05）,and both varieties showed a similar pattern.Ultimately,the HY73 coupled W1 treatment gave the highest yield of 7.03 t·ha^-1,which was 1.05-1.22 times higher than the other combination patterns.2.Compared with HHZ,WDR,HY73 had a more rapid physiological adaptation mechanism to protect photosynthetic organs from injury during drought and rehydration.The maximum net photosynthetic rate(A_max)of HY73 decreased by 36.21%under extreme drought,while that of HHZ decreased by up to 60.73%;after rehydration,the photosynthetic parameters of HY73 fully recovered to the initial state,while the indicators of HHZ could not be fully restored.Correlation analysis showed that HY73 was significantly linearly correlated with ABA and SA,while HHZ was significantly linearly correlated with ABA,IAA and BR（P<0.05）,but not with SA（P>0.05）.3.Light alternating wet and dry irrigation further improved the drought resistance and the post-drought rehydration recovery ability of WDR by optimizing intracellular physiological activities.The performance of the antioxidant enzyme system and osmoregulatory substances between the different water treatments was W1>W0>W2.Two principal components were extracted from the principal component analysis of all physiological indicators,and it was found that the W1 treatment was closely related to the physiological response performance under extreme drought compared to W0 and W2.The first principal component mainly included antioxidant enzymes,osmoregulatory substances,and SA content,while the second principal component was dominated by the content of endogenous hormones ABA,IAA,and BR,which may provide an important physiological basis for maintaining high photosynthetic production potential under drought in WDR under W1treatment,thus ensuring a higher yield.In conclusion,the significantly A_max-related ABA and SA content,the higher POD activityand osmoregulatory substance contents can be considered as the important physiological basis for maintaining the high photosynthetic production potential of HY73,and its higher yield performance in response to drought and rehydration under alternating wet and dry treatments may be related to the regulation of its endogenous hormones..