Effects Of High Temperature On The Boll Development Of Island Cotton During The Flowering And Boll-Forming Stage And Its Photosynthetic Mechanism

With the fluctuation of natural climate and the intensification of human activities,short-term high temperature events occur frequently all over the world.The emergence of extremely high temperature will seriously affect the growth of crops around the world.As a synonym for high-quality natural fiber,the quality of island cotton enjoys a high reputation in the world.Xinjiang is the only island cotton producing area in China.High temperature stress has become an important factor in low yield and poor quality of island cotton in China.A warming shed was set up in the field during the full bloom stage,and treatments of four warming levels[lasting for 0(control),3(H3),6(H6),and 9 d(H9)]were employed to simulate the effects of short-term high temperature stress.The effects of different duration of high temperature on boll development of island cotton were studied.The main results are as follows:1 Effects of high temperature stress at flowering and boll stage on dry matter accumulation,yield and quality of island cottonHigh temperature stress at different time at flowering and boll stage decreased the aboveground dry matter weight of island cotton and the dry matter weight of all organs.However,under the treatment of H6 and H9,the stem and leaf dry matter of Xinhai 43 and Xinhai 49 increased by 32.1%,46.1%and 28.4%,40.4%,respectively.High temperature stress decreased the yield of Xinhai 43 and Xinhai 49,in which H6 and H9 treatments reached a significant level,while high temperature stress significantly reduced the boll number,boll weight and lint percentage of the middle fruit branches,thus reducing the yield.Under high temperature stress,the boll number,boll weight per boll,lint percentage and lint yield in the middle of Xinhai 43 decreased by 33%55%,10.5%,8.8%and 18.6%respectively compared with the control,and Xinhai 49 decreased by 31%82.8%,0.3%24.0%,5.4%10.8%and 18.1%84.7%,respectively.Compared with the control,the bolls of upper fruit branches of Xinhai 43 and Xinhai 49 treated with H6 and H9 increased by 20%,24.9%and 31%,58.2%,respectively,which increased the yield of upper fruit branches by 11.5%,12.7%and 4.3%,11.6%,respectively.High temperature stress had no significant effect on the fiber quality of the two varieties,but there were differences in the fiber quality of cotton bolls in different parts.High temperature significantly decreased the fiber length and breaking specific strength of cotton boll in the middle fruit branch,and increased the specific strength of cotton boll in the upper fruit branch,in which H6 and H9 treatments reached a significant level.compared with the control,it increased by 2.2%,5.1%and 4.5%,1.6%,respectively.Under high temperature stress,the change range of yield and quality of fruit branches of Xinhai 49 was larger than that of Xinhai 43,indicating that the effect of high temperature stress on Xinhai 49 was more serious.2 Effects of high temperature stress at flower and boll stage on bud and boll shedding and boll development of island cottonH3,H6 and H9 treatments significantly increased the bud and boll shedding rates of 2 fruit branches,3 fruit branches and 5-6 fruit branches of two island cotton varieties,respectively.The shedding rate of bud and boll of Xinhai 43 increased by 4.1%.11.0%and 23.2%compared with the control,and the shedding rate of Xinhai 49 increased by 2.6%,13.1%and 22.7%compared with the control,among which H9 treatment reached significant difference.Compared with the two varieties,there was no significant difference in bud and boll shedding rates between Xinhai 43 and Xinhai 49 under different temperature treatments.With the extension of the days of high temperature,the length and volume of cotton bolls decreased gradually,but there was no obvious relationship between the diameter of cotton bolls and the days of high temperature.The decrease of cotton boll volume after high temperature stress is mainly due to the decrease of cotton boll length.Through simple regression analysis,it was found that Xinhai 43 and Xinhai 49 had significant negative correlation with boll length,volume,fiber dry matter mass,cottonseed dry matter mass and high temperature duration.There was a significant positive correlation between Xinhai 43 and Xinhai 49 bell shell dry matter massand high temperature time.Under high temperature stress,the beginning period of rapid dry matter accumulation of bell shell is advanced,the end period is delayed,and the duration is prolonged,which leads to the increase of dry matter quality of bell shell.The beginning and end periods of rapid dry matter accumulation of fiber and cottonseed were advanced,and the duration was slightly shortened,while the maximum accumulation rate decreased significantly,which led to the decrease of dry matter quality.High temperature stress significantly reduced the boll weight of cotton bolls in the middle and upper parts,and there was a significant difference between H6 and H9 treatments.High temperature stress increased the distribution proportion of boll shell and cottonseed in the middle part of cotton boll,but decreased the distribution proportion of fiber,but high temperature stress had no significant effect on the distribution of lower and upper cotton bolls.Correlation analysis showed that higher Pn was beneficial to the accumulation of fiber dry matter,while lower Pn inhibited the migration of assimilates to fiber in boll shell and cottonseed.3 Effects of high temperature stress at flowering and boll stage on photosynthetic physiology of the subtending leaf to island cotton bollWith the extension of high temperature days,the net photosynthetic rate and stomatal conductance of two varieties of island cotton decreased,the intercellular CO2 concentration continued to increase,while the transpiration rate increased significantly under H3 treatment,and decreased under H6 and H9 treatment.After different days of high temperature treatment,the maximal photochemical efficiency,actual photochemical efficiency of PS II and photochemical quenching coefficient of the two varieties decreased in different degrees.However,the decrease of actual photochemical efficiency of PSⅡ and photochemical quenching coefficient is obviously greater than the maximum photochemical efficiency.The decrease of actual photochemical efficiency of PS Ⅱ and photochemical quenching coefficient of Xinhai 43 was less than that of Xinhai 49,but there was no significant difference in the maximum photochemical efficiency between the two varieties of island cotton.The non-photochemical quenching coefficient increased continuously with the extension of high temperature time,and the non-photochemical quenching coefficient of Xinhai 43 was significantly higher than that of Xinhai 49.The attenuation rate of the parameters above the leaves slowed down under H6 and H9 treatments at the later stage of reproductive growth(40 days after anthesis).Showed better photosynthetic characteristics than the control.With the extension of high temperature days,the dry matter of bolls of two varieties of island cotton decreased significantly compared with the control,while at 40 days after anthesis,the dry matter of stems and leaves of two varieties H6 and H9 increased significantly compared with the control.Principal component analysis showed that the increase of dry matter accumulation in stems and leaves in the later stage of reproductive growth could slow down the decrease of photochemical quenching coefficient,actual photochemical efficiency of PSⅡ,stomatal conductance,net photosynthetic rate.To maintain these photosynthetic physiological parameters at a high level.With the extension of high temperature days,the non-photochemical quenching coefficient of Xinhai 43 was significantly higher than that of Xinhai 49.therefore,the non-photochemical quenching coefficient can be used as an important index for screening island cotton varieties with high temperature tolerance.The decrease of effective photochemical quantum yield of Xinhai 49 was mainly due to the decrease of photochemical quenching coefficient,while the decrease of effective photochemical quantum yield of Xinhai 43 boll was due to the decrease of photochemical quenching coefficient and maximum photochemical quantum yield at the same time.Under H6 and H9 treatments,the decrease of effective photochemical quantum yield of Xinhai 43 was accompanied by the increase of regulatory energy dissipation.The higher regulatory non-photochemical heat dissipation of Xinhai 43 was the key protection mechanism of PS Ⅱ from excess excitation energy light damage.