| Producing more food with fewer resources is an important issue that modern agriculture needs to address in the context of climate change.Therefore,the water-saving potential of crops must be utilized more fully to achieve stable yields while increasing water use efficiency.Numerous studies on deficit-regulated irrigation and drought priming have shown that the drought tolerance of wheat can be effectively exploited to ensure yield and improve water use efficiency through appropriate irrigation water management schemes.Different drought-re-watering scenarios(period,duration,degree,and frequency)affect the response of winter wheat to drought and recovery after re-watering,thus affecting yield and water use efficiency.To investigate the physiological response of winter wheat to drought-re-watering and the yield enhancement mechanisms of different water regulation schemes,three winter wheat greenhouse pot experiments were deployed in this study between 2016 and 2020.All experiments were conducted with adequate water supply(75%-85%FC,FC represents field water holding capacity)in the whole period treatment as the control group.The experimental contents were:(1)Tiller-jointing water regulation experiments,including drought-primed treatments with persistent and intermittent drought before jointing(55%-65%FC)-adequate water supply after jointing and gradual drought treatments with gradually decreasing soil water content(100%-34%FC),for a total of three drought treatments.(2)Short-term drought-re-watering experiments after jointing,including three growth stages(jointing-booting,heading-flowering,and filling-maturity)and three drought levels(65%-75%FC,55%-65%FC,and45%-55%FC),for a total of nine drought treatments.(3)The repeated drought-re-watering experiment during the whole growth period was based on the persistent and intermittent drought priming before the jointing stage with the addition of repeated drought-re-watering cycles at the heading and flowering stages,for a total of six drought treatments.The effects of different water management schemes on yield and water use efficiency,growth and development of winter wheat were investigated,and the responses of photosynthesis,antioxidant protection,osmoregulation and hormone regulation to soil water changes were analyzed to investigate the relationship between physiological response mechanisms and growth and development and water productivity.The main findings were as follows.(1)The physiological response of winter wheat to water changes during the tillering-jointing period was revealed,and the effects of different drought priming schemes on growth and yield were clarified.Compared to the control,both drought priming(55%-65%FC)strategies,pre-jointing persistent drought and intermittent drought,induced photosynthetic,growth and yield compensation effects in winter wheat after re-watering to adequate water supply(75%-85%FC)at the jointing stage.Among them,intermittent pre-jointing drought was better regulated than persistent drought.The increase in the number of drought-re-watering cycles increased the upper limit of photosynthetic rate after re-watering at the jointing stage of plants in the priming group and enhanced the correlation between soluble sugars and photosynthetic rate.The photosynthetic rate after re-watering at the jointing stage showed that intermittent drought>persistent drought>control,which was consistent with the ranking of the results of yield and water use efficiency.The variation of soil water content(SWC)in the range of 55%-85%FC did not significantly reduce the aboveground growth capacity of wheat,but wheat started to actively inhibit leaf growth after SWC<55%FC.Exponential decreases in photosynthetic rate and stomatal conductance,exponential accumulation of abscisic acid and osmotic substances,and significant increase in antioxidant protective enzyme activities(R~2=0.795-0.963)were observed during the gradual drought of the tillering-jointing stage.(2)The physiological water-saving potential of winter wheat under short-term post-jointing drought-re-watering conditions was investigated,and the sensitivity of different indicators to soil water changes was assessed.Short-term droughts(45%-75%FC,duration≤9 days)in a single growth period after the jointing stage all caused yield reduction(2.03%-64.39%),with the most severe reduction being the jointing-booting period and drought levels of 45%-55%FC(P<0.05).Drought-re-watering treatments of 55%-75%FC at the heading stage were able to improve the water use efficiency of winter wheat(4.96%-22.4%).Photosynthesis decreased significantly at the drought stage during the different growth stages after jointing and did not return to the control level within9 days of re-watering.The antioxidant enzyme activities showed different degrees of up-regulation,and the proline and soluble sugar contents accumulated significantly during drought within different growth periods after jointing(P<0.05).The contents of all indicators could basically be restored to the control level within 14 days after re-watering.The photosynthetic rate of winter wheat could reflect the status of drought tolerance indicators in wheat during the short-term drought-re-watering process.The relationship between antioxidant enzyme activity and photosynthesis was stronger than that between osmotic regulation.The sensitivity of superoxide dismutase,proline and net photosynthetic rate to changes in soil water was higher(AUC>0.7,P<0.05).(3)Repeated-drought re-watering promoted the photosynthetic compensation effect of winter wheat after flowering,which was beneficial to increase yield and efficiency.The increase in the cycle of drought(55%-65%FC)at heading stage-re-watering(75%-85%FC)at flowering stage could enhance the effect of pre-joining drought priming(55%-65%FC)on yield and improved water use efficiency.However,the positive effects of repeated droughts before jointing and heading stage did not completely offset the negative effects of water deficit at flowering stage.Drought-primed plants that experience a water deficit of 65%-75%FC at flowering stage still reduced yields.Winter wheat that had experienced drought exercise(55%-65%FC)during the vegetative growth period and experienced drought again(55%-65%FC)at the heading stage had no significant decrease in photosynthetic rate,stomatal conductance and transpiration rate.Drought priming before jointing and drought at heading stage improved the drought tolerance of winter wheat still significantly after re-watering at flowering and filling stages.(4)The mechanism of increasing yield and efficiency of winter wheat under the strategies of drought-re-watering at the tillering-jointing stage and repeated drought-re-watering during the whole growth period was elucidated.The response mechanism of winter wheat to water regulation was that drought-re-watering during tiller-jointing optimized aboveground growth through endogenous hormones and promoted photosynthetic compensation after jointing re-watering by improving drought tolerance of winter wheat during drought-re-watering cycle,which facilitated the generation of growth compensation and yield compensation in winter wheat.The enhancement of drought tolerance in winter wheat by drought at the heading stage was not affected by the subsequent re-watering during the repeated-drought process,and was maintained at a high level during the flowering and filling stages.This is an important reason for the photosynthetic compensation effect in winter wheat during the repeated-drought-re-watering process.Compared to the control,the treatment with intermittent drought priming(55%-65%FC)before jointing overlaid with another drought(55%-65%FC)at heading stage(R2)was the most effective among all yield enhancing treatments:plant height and leaf area increased by7.75%and 9.89%,respectively,yield increased by 17.29%,and water use efficiency increased by 28.38%(P<0.05).In conclusion,the persistent,intermittent drought priming(55%-65%FC)before jointing triggered a stress response in winter wheat that facilitated photosynthetic and growth compensation after re-watering at the jointing stage and laid the foundation for winter wheat to better cope with another drought.The stress response of winter wheat under short-term post-jointing drought-re-watering conditions was reversible,and the scheme of drought at heading stage and re-watering at flowering stage was beneficial for water use efficiency.The repeated drought-re-watering strategy of pre-jointing drought(55%-65%FC)combined with heading stage drought(55%-65%FC)was effective in increasing yield and improving water use efficiency. |
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