| Polymethylmethacrylate（PMMA）is a copolymer of methyl methacrylate（MMA）and is a transparent material with excellent overall properties.In recent years,PMMA has excellent transparency,apparent gloss,and arc resistance,as well as good dielectric,electrical insulation,aging,and post-processing properties.It is then widely used in aviation,construction,chemical instruments and other fields.However,there are few studies on the application of PMMA in agriculture.So far,studies on the effects of PMMA as a rain-preventing material on plant growth and fruit flavor quality have not been reported.In this paper,’Dacelaket’strawberries were used as experimental materials to study the effects of two kinds of shelters,PE shelter and PMMA shelter,on their physiological characteristics,fruit flavor quality and microenvironment,in order to find the effects of PMMA shelter on plant physiological characteristics and fruit quality and provide a theoretical and practical basis for the application of PMMA in agriculture.The main findings are as follows:（1）In the three kinds of weather,the temperature in the PMMA shed was numerically greater than that in the PE shed,and the humidity was less than that in the PE shed,but there was no significant difference in temperature and humidity between the two sheds.The light intensity in the two sheds did not reach the significant difference level,but the maximum light transmittance of the PMMA shed was 87.5%,while the PE shed had 89.2%.On sunny days,the light intensity of the two sheds was significantly lower than that of the open ground.On cloudy days,there was no significant difference between the light intensity of the PE shed and the exposed land,but there was a significant difference between the light intensity of the PMMA shed and the open land.In rainy days,the three did not reach the level of difference in significance.（2）In the early stage of plant growth,the differences in stem diameter,plant height,and petiole length were not significant between two sheds.At the late growth stage,the plant growth in the PMMA shed was greater than that in the PE shed.The former was6.24%higher than the latter,and the petiole length was longer,it was 10.34%longer than the latter,but the growth of the plant in two sheds did not reach the level of significant difference.（3）With the growth of plants,the change trends of photosynthetic parameters Ci,Tr,Gs and Pn of strawberry leaves in the two sheds are consistent,and in the case of larger Gs,the corresponding Pn is higher and Ci is lower.During the fruiting period,the Ci value of the PMMA shed was significantly higher than that of the PE shed,and the Tr value was significantly lower than that of the PE shed.During the flowering period and the full red period,the Gs value and Pn value of the PMMA shed were significantly higher than those of the PE shed,and were significantly lower than those of the PE shed.The maximum net photosynthetic rate in the PMMA shed appeared at the bud stage,reaching 16.2μmol·m-2·s-1,while the PE shed appeared at the color change stage,reaching 17.38μmol·m-2·s-1.（4）The Fo,Fm,Fv/Fm,and Fv/Fo of strawberry leaves in the PMMA shed were higher than those in the PE shed,but the difference was not significant.（5）With the development and maturation of the fruit,the strawberry fruits in the two sheds showed the unique color of the strawberry:from green to white and then to red.However,the a*of the fruit in the PMMA shed was significantly greater than that of the PE shed in the first four periods,especially in the color change period,the former being 1.7 times greater than the latter.This shows that the fruits of the PMMA shed are redder than those of the PE shed at the same stage,which means that the PMMA shed accelerates the ripening of the strawberry.（6）There was no significant difference in fruit weight at fruit development stage between the two sheds.The change range of TSS is 5.07-8.47°Brix,and the growth is gentle in the early stage of maturity.From the powder fruit period to the full red period,the TSS of fruits in the PMMA shed grows rapidly,and goes back to the PE shed in the full red period,reaching 8.47°Brix,resulting in significant differences.The change range of the TA of the two treatments was 0.59-1.82%,and the fruit showed a downward trend during the maturation of fruits,but the difference was not significant.The content of Vc in the fruits of the two sheds ranged from 17.19 to 67.35 mg/100 g.It increased with the maturation of fruits and did not reach the level of significant difference.（7）Fructose,glucose and sucrose were the main soluble sugars detected.Among them,fructose dominated.The maximum percentage of fructose in the PMMA shed was43.48%,while the PE shed was 39.83%.In the two sheds,the trend of soluble sugars was consistent with the maturity of the fruit,but the soluble sugar content of strawberry in the PE shed was always greater than that in the PMMA shed.In the PMMA shed,as the fruit matures,the change trend of total sugar is consistent with the change trend of its fructose and glucose.However,the trend of total sugar in PE sheds was consistent with the change trend of sucrose content.It means that soluble sugars of strawberry in PMMA shed were dominated by fructose and glucose,while sugar content in PE sheds was dominated by sucrose content.（8）Oxalate,tartrate,malate and citrate were the important organic acids detected,of which tartrate and citric acid dominated both treatments,and contents of the two acids in the PMMA shed were 11.2-19.63 mg·g-11 FW and 6.89-11.93 mg·g-11 FW,respectively,while the PE shed were:4.58-12.35 mg·g-11 FW and 6.58-14.32 mg·g-1FW.The change trends of oxalate and malate in the two sheds are complex,and there is no fixed regularity of change;with the ripening of fruits,the tartrate shows a tendency of accumulation,and citrate shows a decreasing trend.The mode of variation of organic acids in the PMMA shed was the accumulation of tartrate,whereas in the PE shed,the accumulation of citrate was converted into the accumulation of tartrate.（9）Totally,72 kinds of aroma were identified from two treatments,among them,the main components is aldehydes,ketones,esters and terpenes,and including 27 kinds of esters,11 kinds of terpenes,9 kinds of aldehydes,9 kinds of alkanes,9 kinds of alcohols,4 kinds of acids,2 kinds of ketones and one kind of other substance.During fruit development and maturation,strawberry fruits in the two sheds are transformed from aldehydes containing green apple and grass-like aroma to accumulated esters and ketones that can release fruit flavors and floral aromas.The aroma substances shared in the two sheds include methyl butyrate,ethyl butyrate,butyl acetate,ethyl caproate,ethyl caprylate,butyl butyrate,hexanal,and（E）-2-hexenal,nonyl aldehyde,octanal aldehyde,cis-3-hexenol,linalool,trans nerolidol,γ-decalactone and DMMF.Octyl acetate in the fruits of PMMA sheds was detected at S4 and S5,and the contents were 0.08μg·g-11 and 0.29μg·g-1,respectively,while it was not find PE.2-ethylhexyl acrylate,（3Z）-3-octenyl acetate,ethyl octanoate,hexyl caproate,pentyl caproate,octyl propionate,and decyl caproate were detected in fruits of PE shed,but were not detected in PMMA.（10）Based on the flavor quality of the Pheatmap and PCA model analysis,sugar and organic acids formed the basic flavor of the fruit,and the characteristic aroma had a decisive role in distinguishing the fruit flavors of different rain-shelters.（11）In the correlation analysis between the two rain-shelters,the content of soluble solids in fruits in the PE shed was significantly correlated with the a*value and temperature,but the fruits in the PMMA shed did not show such correlation,indicating that compared to PMMA Shed,fruits in PE shed are more susceptible to environmental conditions.（12）In the analysis of economic benefits,from the third year onwards,the economic benefits of strawberries in the PMMA shed began to go beyond the PE shed,and in the sixth year,it still maintained high economic benefits. |
