The Effect Of Summer High Temperature In Chengdu Plain On The Growth And Physiology Of Magonolia Dawsoniana

In order to explore the effect of summer high temperature on the physiological indicators of growth of Magnolia dawsoniana,under the natural high temperature stress of Chengdu Plain in summer,in July and August,the 3-5-year-old M.dawsoniana grafted seedlings and seedlings,M.denudata and M.liliflora were determined in the high temperature period.The changes of physiological indicators and photosynthetic indexes of seedlings were measured,and the daily changes of photosynthetic indexes of these four kinds of seedlings were measured at the late high temperature in September.The results show:?1?In the high temperature photosynthetic index,the net photosynthetic rate of M.dawsoniana seedlings and grafted seedlings,M.denudata and M.lilifloraincreased first and then decreased.With the persistence of high-temperature stress,several seedlings began to exhibit photosynthetic inhibition on August 13.However,the net photosynthetic rate of grafted seedlings of M.dawsoniana was higher than that of other seedlings at each time period,indicating that grafting increased the light energy utilization efficiency of the leaves of M.dawsoniana;The change trend of stomatal conductance of several seedlings was positively correlated with the change trend of photosynthetic rate.The variation trend of intercellular CO₂ concentration was roughly correlated with the change trend of photosynthetic rate and stomatal conductance,butthe difference of intercellular CO₂ concentration at various time points,but there was no significant difference among the intercellular CO₂concentrations at various time points.From July 13 to August 23,the transpiration rates of the seedlings and grafted seedlings of M.denudataandM.dawsonianashowed a tendency of decreasing first and then increasing.The transpiration rate of M.denudatashowed a relatively slow and continuous increase phenomenon.The transpiration rate of grafted seedlings of M.dawsoniana increased slowly,and the transpiration rate increased with the increase of temperature,indicating that under high-temperature conditions,accelerated transpiration is an effective protective measure for the four seedlings to avoid high temperatureburns on leaves.The results showed that the growth of several seedlings was inhibited by high temperature.M.dawsoniana seedlings and grafted seedlingswere more inhibited than those of M.denudata and M.liliflora.To some extent,according to the above,grafting improves M.dawsonianaseedings'light adaptability.?2?High-temperature physiological indicators.From July 13 to August 13th,the chlorophyll content of the seedlings and grafted seedlings of Kangding,M.M.denudata andM.liliflora showed a trend of increasing first and then decreasing.The protein content of the seedlings and grafted seedlings of M.denudata and M.liliflora slightly decreased first,thenrose rapidly,while the soluble protein content of M.denudata continued to rise;the protein content of the seedlings and grafted seedlings of M.M.and M.liliflora slightly decreased.After that,it rose rapidly,while the soluble protein content of M.denudata increased continuously.The soluble sugar content of M.dawsoniana seedlings and M.liliflora rose first and then decreased.The soluble sugar content of M.dawsoniana grafted seedlings rose first,then decreased,then rose,and the solublesugar content of M.denudata increased.The SOD activity of M.dawsoniana seedlings and grafted seedlings and M.lilifloradecreased first and then increased,and the volatility decreased again.The SOD activityof M.denudata first decreased and then continued to rise.The SOD activity of grafted seedlings of M.dawsoniana changed greatly,followed by M.dawsoniana seedlings,M.denudata and M.liliflora;POD activity of M.dawsoniana seedlings first increased and then decreased,and then increased volatility upward trend,the SOD activity of the grafted seedlings of M.dawsoniana,M.denudata and M.liliflora rose first and then decreased.The POD activity of grafted seedlings of M.dawsoniana changed the most,followed by M.dawsoniana seedlings,M.liliflora,M.denudata.The results showed that the summer hightemperature in Chengdu Plain had a significant inhibitory effect on the growthof grafted and seedlings of M.denudata,M.liliflora showed better heat resistance,but compared with the seedlings,grafted M.denudataseedlings were grafted to a certain degree improved the heat-resistant ability of M.dawsoniana.?3?Take September 10 as an example,during the later period of high temperature,the photosynthetic indexes of M.dawsoniana seedlings at a high temperature of 8:30to 15:30 were all ata lower value,this indicates that under high temperature conditions,the growth of M.dawsoniana seedlings is higher than that of the other three species.Seedlings should be poor,seedlings growing under hightemperature conditions are subject to certain stress;M.dawsoniana seedlings in the time period from 15:30 to19:30 have significant changes in the photosynthetic index,net photosynthetic rate,stomatal conductance and transpiration rates have all increased significantly.These indicators are higherthan thoseof M.denudata and M.liliflora.The temperature began tograduallydecline during this time period,indicating that a certain temperature reduction promoted the growth of the seedlings of M.dawsoniana;the photosynthetic indexes of the grafting seedlings of M.dawsoniana at various times of the day were almost higher than those of the other three seedlings.It showed that the grafted seedlings had better adaptability under the high temperature stress than other three kinds of seedlings;the photosynthetic indexes of the four seedlings decreased at different degrees during the high temperature period,and the net photosynthetic rate decreased to around 15:30,meanwhile,the transpiration rate also dropped to the lowest value around 15:30.The photosynthetic diurnal change inJuly 10th and August10th also showes that the growth ofseveral seedlings wasinhibited under high temperature,and the seedlings and grafted seedlings of M.dawsoniana were inhibited.Compared with M.denudata and M.liliflora,the inhibition of high temperature is more obvious.Grafting improves the light adaptability of M.dawsoniana seedlings to a certain extent.As described in the review,in the natural and high temperature conditions of Chengdu Plain,M.denudata and M.liliflora had better heat-resistance in terms of physiological growth indexes and photosynthetic indexes than grafted and seedling plants of M.dawsoniana.Due to the different growth environment of M.dawsoniana,its high temperature inhibition in Chengdu Plain was exhibited.To a certain extent,grafting increased the growth adaptability of M.dawsoniana.