Effects Of Sunshade Nets Of Different Colors On Growth Environment And Production Performance Of (Capsicum Chinese Jacq.) In Hainan Area

The high temperature and strong light in summer and autumn in Hainan are easy to produce photoinhibition phenomenon,which is disadvantageous to seedling and plant growth of（Capsicum Chinese jacq.）.Therefore,the use of sunshade net can not only effectively alleviate the high temperature strong light,provide a good environment for seeding breeding,but also improve the plant growth and fruit quality.In the seeding stage,five kinds of shade nets of yellow,beige,pearl,red and black were used to regulate the seeding environment and cultivate robust（Capsicum Chinese jacq.）seedings.At the fruiting stage,the growth environment was controlled by shading nets with three colors of pearl,red and black,and two shading rates of 30%and 50%,so as to improve the fruit quality and the content of bioactive compounds.At the same time,the partial least squares regression method and BP neural network algorithm were used to study the influence of environmental parameters on the change of stem diameter at the seedling stage,the change of stem diameter at the fruit stage and the change of fruit diameter,so as to further determine the influence of environmental parameters at each growth stage on the growth of crops.The results are as follows:（1）At 13:00 at noon,the light intensity of pearl shade net was 627μmol·m^-2·s^-1,the air temperature was 32.50℃,and the relative humidity was 36.60%.The shade effect of pearl shade net was the lowest,followed by red shade net,and black shade net was the best.The net photosynthetic rate of‘Rila 2’pearl sunshade net treatment reached（12.37±0.24）μmol·m^-2·s^-1,the stomatal conductance was the highest,intercellular CO₂ mole fraction was the lowest,and transpiration rate was the highest in CK.The transpiration rate of all shading treatments was lower than CK.‘High-hot Capsicum Chinese Jacq.F₁’leaf area and SPAD values of red and pearl shade net treatments were higher than those of the control,and the seedling index of pearl shade net treatment was above 0.27.The highest value of‘Rila 2’was（0.30±0.03）.The biomass of‘Tan tan xiang 3’was significantly lower than that of‘High-hot Capsicum Chinese Jacq.F₁’and‘Rila 2’,and the biomass of‘Tan tan xiang 3’was the highest when treated with pearl and red sunshade net.The soluble sugar content and MDA content of control CK were the highest,but the soluble protein content and root activity of control CK were lower than those of shading treatments.The contents of soluble sugar and MDA were significantly positively correlated with light intensity and air temperature（P<0.01）.The leaf area of pepper was negatively correlated with light intensity and air temperature（P<0.01）.（2）The light intensity of pearl sunshade net with the same shading rate was higher than that of red and black sunshade net.The difference between the light intensity of the pearl shade net with 50%shading rate and the black shade net with 30%shading rate at 12:00 is small.The air temperature of red and pearl shade net with 30%shading rate at 13:00 noon is 34.73℃and 35.28℃,respectively,the smallest difference between them.The biomass and growth of‘Tan tan xiang 3’were lower than that of‘High-hot Capsicum Chinese Jacq.F₁’and‘Rila 2’.The root activity of‘Tan tan xiang3’was the strongest,followed by pepper‘High-hot Capsicum Chinese Jacq.F₁’and‘Rila 2’.The interaction between sunshade net and pepper varieties had great influence on root activity.The fruits length of‘High-hot Capsicum Chinese Jacq.F₁’and‘Rila 2’are longer than those of‘Tan tan xiang 3’.The maximum under the red shading net of30%shading rate of‘High-hot Capsicum Chinese Jacq.F₁’was（47.06±4.59）mm.The single fruit fresh weight was the highest in red and pearl shade nets with 30%shading rate and 50%shading rate,while CK was lower than each shading treatment.The pearl shade net with 30%shading rate had the highest fruit yield per plant,and‘High-hot Capsicum Chinese Jacq.F₁’and‘Rila 2’had the highest fruit quantity per plant under this shade net.The contents of soluble solids,soluble sugar and cellulose in CK were the highest,which were higher than those in shading treatments.The content of Vc andβ-carotene were increased under the pearl shade net,and there was no significant difference between the total phenol content of‘Rila 2’and the flavonoid content of‘High-hot Capsicum Chinese Jacq.F₁’.The total antioxidant activity of‘Tan tan xiang3’was the highest,and the total antioxidant activity of‘Tan tan xiang 3’was the highest under the pearl shade net with 50%shading rate,which was（29.69±2.01）%.In the principal component analysis,fruit weight,Vc content,β-carotene content and total phenol content have the most contribution.The results showed that 30%red shade and50%pearl shade net had the best effect,and the yield,quality and content of bioactive compounds of（Capsicum Chinese Jacq.）were increased at fruit stage.（3）In the partial least squares regression metheod model of pepper seeding stage,the R² between the estimated and true stem diameter changes of red and pearl sunshade net treatments were 0.84 and 0.93,respectively.The root mean square error（RMSE）was 0.056 and 0.032,respectively.In the BP neural network algorithm model,the correlation coefficients R of stem diameter change test error curves treated with red and pearl shade net were 0.92 and 0.93,respectively.The root mean square errors（RMSE）were 0.272 and 0.143,respectively.If the root mean square error of the partial least squares regression metheod model is low,the overall simulation effect of the model is higher than that of BP neural network algorithm model.In the BP neural network algorithm model,the correlation coefficients R of the test error curves of leaf temperature change treated with red and pearl sunshade net were 0.95 and 0.93,respectively.The root mean square error is higher than the partial least squares regression metheod model,and the overall effect is lower than the partial least squares regression metheod model.In the BP neural network algorithm model of pepper fruit period,the correlation coefficients R between the test error curves of fruit diameter change treated with 30%red shade and 50%pearl shade net were 0.93 and0.97,respectively.The root mean square error（RMSE）was 0.313 and 0.637,respectively.However,in the partial least squares regression metheod model,the the R²between the test error curves of fruit diameter change treated with 30%red shade and50%pearl shade net were 0.96 and 0.95,respectively.The root mean square error（RMSE）was 0.785 and 0.640,respectively.The root mean square error value of BP neural network algorithm model is lower than partial least square method,and the simulation effect of BP neural network algorithm model is better.In the result period,the partial least squares regression metheod model is better than BP neural network algorithm model in predicting stem diameter change and leaf temperature simulation.From what has been discussed above:Red and pearl shade nets have a good shade effect on the growth of pepper seedings;The red shade net with 30%shading rate and pearl shade net with 50%shading rate increased the fruit quality content and biological activity content at the fruiting stage;The the partial least squares regression metheod model was better than the simulation of stem diameter change at seedling stage,and the BP neural network algorithm model was better than the simulation of fruit diameter change at the result stage,which provided a theoretical basis for the model of productive seedlings and fruit yield at seedling stage.