Effects Of Net Shedding On Growth Of Lemon And Fruit Quality

Guangdong Province is a citrus Huanglong disease epidemic area.Planting citrus disease-free seedlings was an effective way to prevent pests and transmission of diseases and it is also an inevitable way for citrus organic cultivation in our province.Therefore,research on citrus net Shed cultivation has great theoretical and practical significance.This study was conducted at the Lemon Modern Industrial Park in Heyuan City,Guangdong Province from February to October of 2017.The test was conducted with Ulek lemon as the research material.The 40-hole steel frame was used as the greenhouse cultivation and the open field cultivation was used as the control.The effects of netting cultivation on environmental factors,plant growth,phenological period,fruit quality and aroma were studied to provide a theoretical basis for the further of lemon cultivation in net sheds.The main findings are as follows:(1)Shed cultivation significantly increases the temperature and humidity in the shed.During the test period,the temperature and humidity of the air and soil in the greenhouse were higher than those in the open ground.The daily change of the air temperature inside and outside the net shelter was inverted U-shaped,that is,the temperature increased first and then decreased,and the daily change in air humidity was U-shaped,that is,the relative humidity dropped first and then increased.The net shelter has a certain shading effect,and the illumination of the tree is 324.8 lux,which is 23.0% lower than that of open cultivation.Shed cultivation has significantly changed the environmental factors of lemon growth,providing with a high temperature,high humidity and relatively shady growth environment.(2)Shed cultivation promotes vegetative growth and reproductive growth.The height of the 4 year old tree was 237.8 cm,which was 10.0% higher than that of the exposed land.The stem diameter was 42.3 cm,31.3% larger than the open land,and the crown width was 308×298.6 cm,which was significantly larger than the open area 264.6×267.4 cm.In addition,the buds and leaves of net-shed plants grew better than open field.The length of buds under net-shed cultivation were 1.01 cm,17.4% longer than bare land,and the width of flower buds were 0.33 cm,and 13.8% larger than open land.The length of spring leaves and summer leaves under the netting cultivation was 10.9 cm and 13.1 cm,which were 11.2% and 17.0% longer than the open land respectively.The difference between treatments was significant,but the change of the length of autumn leaves was not obvious.Shed cultivation also changed the phenological period of the plant.The sprouting period of spring buds was 4 days earlier than that of bare land.The growth period of summer shoots was 4 to 6 days earlier than the open land.The flowering period was about 2 days earlier,and the period of fruit coloring was the same,but the net shed matured 8 days in advance.(3)The net photosynthetic rate(Pn)of lemon leaves in net shelters and open field cultivation are all typical double peak curves.There was a “midday break” phenomenon at noon.The net photosynthetic rate(Pn),transpiration rate(Tr),and stomatal conductance(Gs)of the cultivated leaves were all higher than those of the net shed.The Pn and Gs values of the open field and net shed cultivation were significantly different at 10:00 am.The comparison of photosynthetic in leaves revealed that the contents of chlorophyll a(?a),chlorophyll b(?b),and total chlorophyll(a+b)(?T)were lower than those in open field cultivation,but they were not significantly different.(4)The contents of N,P,K,Mg,Zn,and Ca in spring shoots,summer shoots,and autumn shoots were measured.The content of N and Mg in leaves was the most stable,and there was no significant difference in the changes of leaves of different treatments and different tip times.The content of P and K in the greenhouse cultivation was lower than that in the open field,and the contents of P and K in the summer shoots were 66.7% and 38.0% lower than those in the open cultivation,respectively,all reaching significant differences.The contents of Ca in spring leaves and summer leaves were higher than those in open fields,but the contents in autumn leaves were the opposite;the contents of Zn in spring leaves and autumn leaves were lower than that in open fields,and the Zn content in summer leaves was significantly higher than that in open fields.(5)Shed cultivation was conducive to fruit growth and yield.The longitudinal diameter of mature fruits was 8.54 cm,which was 10.1% higher than open land,6.34 cm in transverse diameter,and 4.5% more than in bare land.The average fruit weight was 160.94 g,which was 19.4 % higher than open land.The average yield per plant was 34.5 kg,which was significantly higher than the 21.8 kg in the open field.In addition,the cultivation of net huts was conducive to improving the appearance quality of fruits.The L value of fruit surface gloss was 59.78,which was 14.1% higher than that of exposed land.The values of a and b were slightly larger than that of exposed lands,indicating that the fruit surface was brighter and the skin color was more orange.The contents of TSS,sucrose,reducing sugar and organic acid in the net awning cultivated fruits were higher than that of the open cultivation in different degrees.In addition to the reducing sugar content,other indicators did not reach significant differences.The content of vitamin C in the early stage of netting fruit development was higher than that of open field,and it was lower than that of open field fruit as the fruit matured.(5)There are 30 kinds of lemon peel aroma components in the net shed,and the richness is relatively low.There are 5 species less than those in the open-cultivated fruits(35 species),mainly lacking ?-sesquidine,?-limonene,n-octylaldehyde,perilla Aldehydes and undecanes.The cultivation of greenhouses in facilities significantly reduced the content of alcohols and aldehydes in fruits,which was reduced by 31.2% and 20.4%,respectively,compared to open cultivation.The content of olefins in facilities cultivation(91.14%)was slightly higher than that in open cultivation(88.8%).mainly due to the higher content of(+)-thromene.