摘要:作物对干旱的响应已有大量研究，但对不同强度干旱及其持续时间响应过程的研究甚少。通过开展全生育期干旱和拔节后干旱过程的影响模拟实验，试图揭示夏玉米叶片光合生理特性对不同干旱强度及其持续时间的响应机理，为我国北方地区玉米育种和节水灌溉提供科学的理论依据。研究结果表明：1）干旱显著降低了玉米叶片的叶绿素相对含量（SPAD），但两种干旱处理下的SPAD随干旱持续时间的延长而出现响应差异并逐渐扩大；2）不同强度、不同持续时间的干旱处理均明显抑制了玉米叶片的最大净固碳速率（A_sat），拔节后的轻度干旱过程对玉米叶片A_sat的影响最大；3）拔节期后重度干旱过程处理下玉米叶片虽保持较高的光合速率，但叶片数量急剧减少，而且一直保持在营养生长阶段，没有产量；4）在两种干旱处理方式下，玉米叶片PSⅡ的光化学效率（F_v'/F_m'）均到灌浆中期才开始出现显著降低现象，表现出了较强的干旱适应能力；5）SPAD与叶片光合及叶绿素荧光参数均存在较强的相关关系，可作为评价玉米叶片光合性能对干旱胁迫敏感性的指示性指标；6）不仅干旱强度影响玉米叶片的生理生态过程，干旱发生的时间也具有重要的影响。



Abstract:Drought is one of the major factors inhibiting maize growth and yield. Thus, studying the effects of drought on maize is particularly important. However, there are few studies examining the effects of the timing and intensity of droughts on maize leaf photosynthetic characteristics, and how the stability and size of maize yields can be hampered in such dry environments. A field automatic rain-shelter was used in this study, and five irrigation treatments, including control and drought stress, were designed. The study aimed to provide a theoretical scientific basis for maize breeding and water-saving irrigation in North China. 1) Drought during the whole growth period and after the jointing stage significantly reduced the leaf chlorophyll relative content (SPAD) of maize, and severe drought treatments had a greater effect on SPAD than mild drought treatments. A difference was observed in the response trends under different drought treatments along with the duration of drought, reflecting differences in the adaptive response of maize leaves to drought. The SPAD of maize leaves under drought after the jointing stage was higher than that in the leaves under drought for the whole growth period, revealing a significant effect of adequate water supply before jointing stage on nutrient accumulation for later leaf growth. 2) Drought during the whole growth period and drought after the jointing stage significantly inhibited the light-saturated net photosynthetic rate (A_sat). Severe drought had a greater impact on A_sat than mild drought in the whole growth period. However, mild drought after the jointing stage had a greater influence on A_sat than severe drought, indicating a difference in the responses of A_sat to different drought treatments. The A_sat under mild and severe drought after the jointing stage was higher than that under severe drought during the whole growth period, revealing that adequate water supply before the jointing stage is very important for maize to adapt to later drought conditions and enhance its photosynthesis. 3) Although the leaves kept a higher A_sat under severe drought conditions after the jointing stage, the total number of leaves per plant reduced sharply, resulting in lower photosynthetic product. The whole maize plant maintained its vegetative growth stage in the whole growth period but with no yield. 4) Under all drought treatments, the photochemical efficiency of PSⅡ in the light (F_v'/F_m') presented the same response regularity. A significant decrease was not observed until the mid-milking period, and then a gradual increase was seen in the late milking period, suggesting a stronger adaptive capacity to drought. 5) SPAD had strong correlations with the leaf photosynthetic and chlorophyll fluorescence parameters, revealing that SPAD could reflect changes in the PSⅡ photochemical activity and photosynthetic capacity of maize under drought conditions, which could be used as an indicator of maize's sensitivity to drought stress. 6) Not only the drought intensity, but also the timing of drought occurrence significantly affected the physiological and ecological processes of maize leaves; therefore, the two factors should be taken into consideration together in future drought studies.





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