Effects of low temperature and weak light combined stresses on photo-synthetic physiological characteristics of watermelon
In order to study the effects of low temperature and weak light on the photosynthetic physiological characteris-tics of watermelon,the watermelon variety Zaojia(8424)was used as the material,and three different temperature(10,15,25 ℃)and two different weak light stresses(100,200 pmol·m-2·s-1)were used to investigate their effects on the morphology,photosynthetic indicators,and antioxidant enzyme activity of watermelon seedlings.The results showed that different low temperatures,weak light,or low temperature and weak light combined stresses significantly inhibited the growth of watermel-on seedlings.Compared with the control,the plant height,stem diameter,leaf area,fresh mass,dry mass,root fresh mass,and dry mass of seedlings after 7 days of low temperature and weak light combined treatment(10 ℃,100 pmol·m-2·s-1)decreased by 28.7％,29.7％,39.1％,43.6％,60.0％,68.8％,and 47.7％,respectively.The maximum photochemical effi-ciency(Fv/Fm)and photochemical quenching coefficient(qP)of PSII both showed a decreasing trend under low tempera-ture and weak light combined treatment.The content of chlorophyll a and total chlorophyll(Chl a+b)decreased,while chlorophyll a/b increased.There was no significant difference in the changes of chlorophyll b content under all treatments.The net photosynthetic rate(Pn),stomatal conductance(Gs),and transpiration rate(Tr)significantly decreased overall under low temperature and weak light treatment,while slightly increased under weak light stress,but still significantly lower than the control.The intercellular CO2 concentration(Ci)and malondialdehyde(MDA)content both significantly increased.In total,low temperature and weak light affect the growth of watermelon.Under low temperature conditions,weak light stress has the greatest impact on the root growth of watermelon seedlings;while under weak light conditions,the lower the temperature,the greater the impact on the aboveground growth and photosynthetic rate of watermelon seed-lings.
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