Response of photosynthetic physiological parameters of maize to drought during the whole growth period and after the jointing stage

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(Asat). Severe drought had a greater impact on Asat than mild drought in the whole growth period. However, mild drought after the jointing stage had a greater influence on Asat than severe drought, indicating a difference in the responses of Asat to different drought treatments. The Asat 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 Asat 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（Fv′/Fm′） presented the same response regularity. A sign