The Effects Of The Enhanced UV-B Radiation On The Fruit Yield And Quality And Photosynthesis Of Mango

The atmospheric ozone depletion and seasonal variation in ozone concentration form the ozone hole may increase the UV-B radiation dose on the surface,and then the UV-B radiation is called enhanced UV-B radiation(or UV-B radiation enhancement).The enhanced UV-B radiation is one of the global environmental problems,and it may damage plant morphology,photosynthesis,plant protection mechanism,DNA and the agricultural ecological environment and so on,so the research on its biological effects has become a hot field in recent years.The effects of the enhanced UV-B radiation on perennial woody plants are researched less at present,in particular,the results about physiological and biochemical mechanisms on the effects of the enhanced UV-B radiation on perennial woody plants during anual period are reported rarely.Cultivation performance and photosynthesis of mango(Mangifera indica)adult trees under the enhanced UV-B radiation are studied,then the characters of the damages of trees can be pinpointed,so it makes a theoretical basis for formulating the reasonable techniques of mango cultivation against the stress of the enhanced UV-B radiation in the futre.Tainong NO.1 mango adult trees were used as experiment materials.The trees used as check(CK)were planted under the sunlight only,and the trees used as treatments were planted under the sunlight and the enhance UV-B radiation.The levels of the enhanced UV-B radiation treatments included 6 linear gradient intensities such as 20 W,40 W,80 W,120 W,160 W and 200 W.The yield of single tree and the photosynthetic indexes of mature leaves were measured in the field,and the physiological indexes of mature leaves and the normal qualities of fruits were determinated in the lab.The main results are displayed as follows:(1)The yield of single tree of the each treatment 160W and 200W got lower than that of CK,while those of the other treatments made no significant difference from that of CK.(P>0.05,the same as below).(2)The contents of soluble sugar and Vc and the ratio of sugar/acid in fruits decreased with the increases of the intensities of the enhanced UV-B radiation,meanwhile,the ratio of sugar/acid in fruits of the every treatment made significant difference from that of CK,except for 20 W treatment in 2016.The content of the soluble sugar in fruits of the every treatment over 80 W got significantly different from that of CK,and the content of Vc in fruits of the every treatment over 120 W was significantly different from that of CK.The contents of the total acids in fruits increased with the increases of the enhanced UV-B radiation intensities,and the differences between the every treatment over 80 W and CK became significant.(P<0.05,same as below).(3)On the whole,the contents of chlorophyll and carotenoid in the mature leaves and the net photosynthetic rate(Pn),the transpiration rate(Tr)and the stomatal conductance(Gs)of the mature leaves decreased with the increase of the enhanced UV-B radiation dose.After November 13th or 26th in 2015 and after February 15th in 2016,the differences of the former 5 ones between the every treatment over 80W and CK were significant(P<0.05,the same as below).(4)The MDA content and the relative conductivity of the leaves increased with the increase of UV-B radiation dose,and the MDA contents and the relative conductivities of the treatments over 80 W were all significantly higher than those of CK.(5)The activities of SOD,POD,CAT in leaves rised first and decresed late with the increases of the enhanced UV-B radiation dose,and the differences of the former 3 ones between the every treatment over 80W and CK were significant after November 13th or 26th in 2015 and after February 15th in 2016.(6)The contents of Flavonoids,polyphenols and reduced GSH in leaves increased with the increases of the enhanced UV-B radiation dose,and the differences of the former 3 ones between the every treatment over 80W and CK were significant after November 13th or 26th in 2015 and after February 15th in 2016.The content of Vc in leaves decreased with the increases of UV-B radiation dose,and the differences of the contents of Vc between the every treatment over 80W and CK were significant after November 13th or 26th in 2015 and after February 15th in 2016.In sum,the enhanced UV-B radiation made the yield of mango adult trees reduce and the qualities of mango fruits get worse,and the causes maybe was that the photosynthesis and transpiration of leaves were inhibited through the cell membrane damaged by the enhanced UV-B radiation.The trees also stayed hydrated by loosening transpiration,then they avoided the damages as possible as they could do.The influences of the enhanced UV-B radiation mentioned above appeared dosage effects and cumulative effects.