The Impact Of Plastic Film Mulch On The Fruit Quality,Sugar And Organic Acid Metabolism In Citrus Maxima 'Hongrou-miyou'

Citrus maxima‘Hongrou-miyou'is mutated from Guanxi pomelo and suitable for cultivation in areas with good temperature and light conditions.In this experiment,5year old‘Hongrou-miyou'in Meixian city,Guangdong province was used as material.The growth environmental factors?weed biomass,soil water potential,soil temperature,tree bore light intensity,tree chamber temperature?,the photosynthetic characteristics?net photosynthetic rate,transpiration rate,stomatal conductance and intercellular CO₂concentration?and the quality of‘Hongrou-miyou'fruit?diameter,single fruit weight,chlorophyll content of peel,peel color value,pulp soluble solids,pulp titratable acid,pulp sucrose and citric acid?were determined after plastic film mulching.The activity of sugar metabolic enzymes?acid invertase,neutral invertase,sucrose phosphate synthase,sucrose synthase?and the activity of acid metabolic enzymes?citrate synthase,malic dehydrogenase,malic acid enzyme,urinase and phosphoenolpyruvate carboxylase?were determined.The effect of ground reflective film mulching on the quality of‘Hongrou-miyou'was preliminarily studied.The main results were as follows:1.Effects of plastic film mulching on environmental factors of‘Hongrou-miyou'.The plastic film mulching obviously inhibited the growth of weeds in plastic covered areas.After 2 weeks of plastic film mulching,the soil water potential of plastic film mulching was lower than the control.After 60 d plastic film mulching,the soil temperature of the plastic film mulching began to be higher than the control,but the difference did not increase further.Generally speaking,plastic film mulching had no effect on the temperature inside the tree canopy,but significantly increased the light intensity inside the tree canopy.2.Effects of plastic film mulching on photosynthetic characteristics of leaves of‘Hongrou-miyou'.The plastic film mulching treatments increased the net photosynthetic rate of the inner leaf at 10:00¹4:00.The plastic film mulching treatments also increased the transpiration rate and stomatal conductance of the inner leaf at 6:00¹2:00 and the intercellular CO₂ concentration at 8¹0.The plastic film mulching increased stomatal conductance and accelerated leaf gas exchange efficiency,which corresponded to the increase of net photosynthetic rate and transpiration rate.The net photosynthetic rate of the canopy leaves was inhibited at 8:00¹2:00,while the transpiration rate and intercellular CO₂ concentration of canopy leaves were increased at 8:00¹0:00,and there was no obvious influence on the stomatal conductance.3.Effects of plastic film mulching on fruit quality of‘Hongrou-miyou'.The plastic film mulching had no significant effect on fruit vertical and horizontal diameter,single fruit weight,peel chlorophyll content and peel color value.The effect of plastic film mulching on the soluble solids and total sugar of‘Hongrou-miyou'was not obvious.But in the early stage of plastic film mulching,the sucrose content of pulp increased,and the content of titratable acid and citric acid decreased at the later stage of plastic film mulching.The ratio of solid to acid was increased.4.Effects of film mulching on enzyme activities related to sugar and acid metabolism of‘Hongrou-miyou'.The enzyme activity of sucrose synthase?synthesis direction?was improved by the treatment reflective film with no hole.The enzyme activity of sucrose phosphate synthetase was increased and the enzyme activity of acid invertase was decreased in the later stage of film mulching.But there was no obvious effect on the activity of acid invertase,neutral invertase and sucrose synthase?cleavage direction?.The fruit development and maturation are mainly sugar accumulation,and the activity of sucrose synthase?synthetic direction?and sucrose phosphate synthetase is also increasing,which is similar to sugar accumulation.The enzyme activity of citrate synthase and enol pyruvate carboxylase was improved at the later stage of film mulching.The film mulching treatment had no obvious effect on the activity of malate synthase,malate dehydrogenase and uratase.Citric acid synthase increased first and then decreased,which corresponded to fruit acid accumulation.The decrease of acid content in‘Hongrou-miyou'is the result of regulation of acid metabolism related enzymes.Citrate synthase was the starting enzyme of three carboxylic acid cycle.The citric acid synthase could participate in the cycle of three carboxylic acid.The citric acid synthase activity of‘Hongrou-miyou'was higher than the control,but the content of titratable acid and citric acid were decreased.