Study On The Mechanism And Simulation Of The Effect Of High Temperature In The Seedling Stage On The Growth And Fruit Quality Of Strawberry

Strawberry planting has become one of the fastest-growing emerging industries due to its short cycle,and high economic benefits.High temperature is the main environmental factor restricting strawberry plant growth and fruit quality in greenhouse.In this study,the strawberry variety"Benihoppe"was used as the experimental material.Cultivation experiments were carried out from September 2018 to January 2019 and from September2019 to January 2020 at the Agricultural Experiment Station of Nanjing University of Information Engineering after treatments with different high temperatures(32/22°C,35/25°C,38/28°C and 41/31°C;daily max/daily min)and different durations of days(2d,5d,8d and11d),with 28/18°C as control.By measuring photosynthetic physiological and biochemical characteristics of strawberry leaves(photosynthetic and anti-aging characteristics),growth and development data(developmental stage,leaf area and dry matter of each organ)and intrinsic fruit quality(vitamin C,soluble sugars,titratable acids and anthocyanins),key heat stress indicators for greenhouse strawberries were extracted,heat stress levels were established and a model was constructed for the effects of heat in seedlings on strawberry fertility,dry matter production and distribution and fruit quality.The results showed that(1)Determination of high temperature stress level of strawberry seedlings.With increasing temperatures and durations,Chla,Chlb,Car,LSP,P_max,AQE and F_v/F_m showed a decreasing trend,while LSP and Rd showed an increasing trend.High temperatures impeded PS II energy transfer(?W_OK>0),accelerated the rate of reduction of the terminal electron acceptor pool of PS I and deactivated the oxygen-evolving complex(OEC)at 11d of stress(?W_OJ>0),except at 32°C.The reactive oxygen species and MDA content tended to increase with increasing days of stress,while the activities of antioxidant enzymes and soluble protein content tended to increase and then decrease under each high temperature treatment.Chla,P_max,?(P_o),PI_abs and MDA were extracted as key indicators by principal component analysis and the high temperature stress index(Z)was calculated.The high temperature stress was classified into mild(2?Z>1),moderate(3?Z>2),severe(4?Z>3)and extra severe(Z>4)based on the Z value.(2)Simulation of the effect of high temperature at seedling stage on strawberry growth period.Mild and moderate high temperatures at seedling stage promoted the strawberry to enter the flowering period,fruit-setting period and picking period earlier,while severe and extra sevre heat delayed the entry of strawberries into these critical fertility stages.Compared with the TEP model and GDD model,the high temperature impact model based on the PDT was more accurate and had the smallest error.The R² between the simulated values and the measured values of flowering stage,fruit setting stage and harvesting stage were 0.84,0.82and 0.97,respectively,the RMSE were 1.39d,1.50d and 1.56d,respectively,the RE were2.27%,2.23%and 1.57%,respectively.Therefore,it is recommended to use the PDT model to predict the start and end times of the strawberry flowering stage,fruit-setting stage and harvesting stage.(3)Simulation of the effect of high temperature at seedling stage on leaf area index of strawberry.Based on the PDT model,a prediction model of the effect of high temperature at the seedling stage on the LAI was established and verified by independent experiments.Based on the model,the R²,RMSE and RE of between the simulated value and the measured value of the LAI were 0.98,0.04,and 6.43%,respectively.Therefore,the constructed model can accurately predict the dynamic changes of the leaf area index after high temperature in the seedling stage.(4)Simulation of the effect of high temperature at seedling stage on aboveground dry matter production and distribution of strawberry.Based on the PDT model,a prediction model of the effect of high temperature in the seedling stage on the aboveground dry matter index was established.Combining this model and LAI model with the SUCROS model based on photosynthesis,a prediction model of the effect of high temperature at the seedling stage on the production and partioning of dry matter above the ground of strawberry was finally established,and verified by independent experiments.The R²,RMSE and RE of between the simulated and measured values of the total dry matter on the ground were 0.91,1.38 g m^–2,and 11.49%,respectively.The R² between the simulated and measured dry weights of leaves,stems and fruits were 0.96,0.93 and 0.98,respectively,the RMSE were 6.62,10.84 and 11.07g m^–2,and the RE were 7.96%,11.42%and 13.97%.Therefore,the constructed model can accurately predict the dry matter production and partioning of strawberries after high temperature in the seedling stage.(5)Simulation of the effect of high temperature at seedling stage on comprehensive internal quality of strawberry.Based on fuzzy mathematics,the entropy weight method was used to determine the weight of the intrinsic quality of strawberry fruit after high temperature at the seedling stage:titratable acid(0.33)>anthocyanin(0.25)>vitamin C(0.23)>soluble sugar(0.19).The scores of the fuzzy comprehensive evaluation showed that the comprehensive scores of the internal fruit quality under mild and moderate high temperature treatments at seedling stage were higher(both greater than 0.6),and the scores were lower under severe and extra severe high temperature treatments(0-0.6).The R²,RMSE and RE of the simulated and measured values of strawberry comprehensive quality based on the constructed comprehensive quality model for were 0.85,0.01 and 19.55%,respectively.Therefore,the constructed model can accurately predict the comprehensive internal quality of strawberry fruit under high temperature in the seedling stage.In short,this study used the simulation of the high temperature scenario of strawberry seedlings,extracted key physiological and biochemical indicators,and determined the high temperature stress level of strawberry seedlings based on dynamic information such as high temperature stress intensity and duration,and built a bridge for better integration with the meteorological service system.The constructed model comprehensively considers the effects of temperature,radiation,photoperiod and high temperature stress factors,which can predict the dynamic effects of high temperature at the seedling stage on the growth period,leaf area,dry matter production and partioning of aboveground organs,and fruit quality of greenhouse strawberries.The mechanism was strong,the parameters were few and easy to obtain,which lays a model foundation for quantitatively evaluating the influence of high temperature weather events on strawberry growth and fruit quality.