Response Of Greenhouse Tomato To The Coupling Of Temperature And Carbon Dioxide

High temperature stress often occurs in tomato production in greenhouses.Many large greenhouses often adopt a production method that avoids summer production,resulting in the use of solar thennal resources that cannot be used in summer.This is an important reason for the difficulty in increasing the yield of greenhouse tomato in China.In this study,the effects of increasing CO₂ application at high temperature on the mitigation effects of greenhouse tomato high temperature hazards were tested.The experiment was conducted in a natural light growth room（length 3m,width 2.4m,height 1.5m in south roof,2.3m in north roof）.The tomato variety ’sapphire’ and ’Hongtu’ were selected as experimental materials.Two tests were conducted in fall 2016 and summer 2017.A high temperature of 30-40℃ was as the treatment while the normal temperature of 20-30℃ as the contrast.Under the condition of each temperature,a normal CO₂ concentration（300-400μL/L,denoted as C1）and a high CO₂ concentration（600-900μL,denoted as C2）were enriched.The following results are drawn:1.Under the treatment of two CO₂ concentrations,plant height and leaf area were all decreased at high temperature compared with normal temperature.After the addition of CO₂,the plant height,stem diameter and leaf area of tomato increased at high temperature and normal temperature,but the increase range was different.High temperature increased the vertical and horizontal diameter of tomato fruit,and low temperature had little effect on horizontal and vertical diameter of tomato.2.Under the treatment of two CO₂ concentrations,compared with the normal temperature,the high temperature treatment reduced the soluble sugar content in the leaves by 6.5%to 10.0%,and the starch content in the leaves decreased by 11.9-29.7%.Under high temperature,increasing the application of CO₂ increased the content of soluble sugar in leaves of tomato by 6.5%,and the content of starch in leaves increased by 36.6%.At normal temperature,the content of soluble sugar and starch in leaves of added CO₂ also increased,but the increase was not obvious.3.Under the treatment of two CO₂ concentrations,compared with normal temperature,the net photosynthetic rate and stomatal conductance of tomato treated with high temperature decreased by about 25-62%and 20-328%,respectively.With the increase of CO₂,net photosynthetic rate and stomatal conductance of tomato increased by 29-66%and 16-253%,respectively.Atnormal temperature,only the intercellular CO₂ concentration in leaves increased by about 10%.4.Under the treatment of two CO₂ concentrations,compared with the normal temperature,the activities of SOD enzyme and MDA enzyme in the high temperature treatment were 125.0-126.4%and 117.5-130.3%lower than those in the control,while the POD enzyme activity was 44.5%lower than the control in the early period,and the later period was 12.2-14.0%higher thanr control.After the application of CO₂,the leaf SOD activity at the high temperature was 10.3%lower than that of the control at the early stage and was similar in the later period.However,the activity of the POD enzyme first decreased by 28.0%and then was similar.The MDA decreased by 54.1%and then increased by 21.3%.CO₂ was increased at room temperature,SOD,POD,and MDA increased by 32.5%,10.9%,and 21.3%,respectively.5.Under the treatment of two CO₂ concentrations,compared with the normal temperature,the content of soluble solids,organic acids and starch,vitamin C and soluble proteint in tomato fruits decreased by 5.5-6.4%,14.3-16.7%and 61.1-62.9%,19.3-37.5%and 13.7-26.8,respectively.It has little effect on soluble sugar content.After adding CO₂ of high temperature,tomato soluble solids,organic acid content,soluble sugar content,starch,vitamin C and soluble protein content increased by 2.9%,8.2%,9.6%,and 16.6%,42.0%and 28.0%,respectively.At normal temperature,increased by 6.0%,19.1%,10.1%,and 18.4%,31.0%,24.0%,respectively.6.Compared with the normal temperature,the fruit ripening period was become earlier,moreover the average yield of per plant was 34%higher in the first three months.At the end of the experiment,however,the yield per plant in high temperature treatment was close to that in normal temperature treatment.After CO₂ enrichment at high temperature treatment,the increase of yield was not obvious.When CO₂ was enriched at normal temperature treatment,the yield was increased by 13%.In summary,the growth and development of tomato are hindered under high temperature,and the plant height,stem diameter,number of leaves,and leaf size are all decreased.The contents of soluble sugar and starch in tomato leaves decreased,and the activities of protective enzymes were affected.The quality of fruits was reduced and the photosynthetic rate was decreased.After application of CO₂,tomato growth,photosynthesis,and fruit quality were improved at room temperature;under high temperature,application of CO₂ increased tomato growth and fruit quality.Therefore,the application of CO₂ can alleviate the high-temperature hazards and improve the fruit quality.