增强UV-B辐射对杧果叶片光合生理和超显微结构的影响

Effects of enhanced UV-B radiation on photosynthetic physiology and ultrastructure of leaves in mango(Mangifera indica L.)

【目的】探讨紫外(UV-B)辐射胁迫对杧果生物量、叶片光合生理和细胞超微结构的影响。【方法】采用2年生三年芒和马切苏杧果树为材料,以自然光照为对照(CK),设置2种不同强度的UV-B辐射(T1:2.5 kJ·m^(-2)·d^(-1)和T2:5.0 kJ·m^(-2)·d^(-1)),测定植株生长、叶片光合参数和细胞超微结构。【结果】2个品种的杧果树对不同UV-B辐射强度的响应存在显著差异。与CK相比,T1、T2处理下三年芒的生长发育、叶片光合色素含量和光合特性指标呈增加趋势,而马切苏下降。随着UV-B辐射的增强,叶片细胞超微结构遭到不同程度的破坏,T1处理下2个品种的杧果叶片表皮蜡质增多,气孔萎缩,叶绿体趋向于椭圆形,积累较多嗜锇颗粒,其中马切苏局部出现断裂,细胞内有大量黑色脂滴形成;T2处理下马切苏细胞结构层次排列不清,黑色脂滴数量显著增加,叶片光合能力降低。【结论】叶片质地较厚的三年芒对UV-B辐射具有较高的耐受性,而叶片质地较薄的马切苏对UV-B辐射具有较强的敏感性,因此三年芒较马切苏更适合于在UV-B辐射较强环境下栽培。

【Objective】With the deterioration of global climate,the attenuation of stratospheric ozone results in the enhancement of ultraviolet(UV-B)radiation on the surface of the earth,which has a wide impact on the physiology and growth of surface plants.In recent years,there were extensive studies about the adverse effects of enhanced UV-B radiation on the leaf structure and photosynthesis in mango,but few research have been carried out to compare the impacts of UV-B on mango varieties with different leaf texture.Thus,the objective of this study was to explore the effects of enhanced UV-B radiation on the growth and development,photosynthetic physiology,and leaf ultrastructure of two mango varieties with different leaf texture,so as to provide reference for the selection of mango varieties with UV-B radiation tolerance under dry and hot valley climate.【Methods】The field experiments were conducted in an experimental orchard of Institute of Tropical Eco-agriculture,Yunnan Academy of Agricultural Sciences from November 2018 to March 2020.Two-years-old mango seedlings cultivar Sannianmang and Maqiesu were used as experimental materials to investigate their leaf texture and response to UV-B treatments.Three UV-B radiation intensities were sett,including natural radiation(CK),and two enhanced UV-B radiation on the basis of natural light,which were 2.5 kJ·m^(-2)·d^(-1)(T1)and 5.0 kJ·m^(-2)·d^(-1)(T2),respectively.The outdoor rainproof lamp holder and 40 W ultraviolet lamp were used to simulate and supplement the UV-B radiation.The distance between the lamp and mango canopy was kept at 0.6 m.The mango canopy was irradiated for 6 h every day from 9:00 to 12:00 and14:00 to 17:00(irradiation was suspended in rainy days),and the irradiation lasted for 16 months.The measurement indices included the growth and development,photosynthetic pigment content,photosynthetic characteristics,light response curve,fluorescence induction kinetic parameters,and leaf ultrastructure.【Results】There were significant differences in growth and development,photosynthetic pigment content,photosynthetic characteristics and leaf ultrastructure between the two mango varieties under different UV-B radiation intensity.Compared with CK,the increment of the plant height,stem diameter and leaf number of Sannianmang significantly increased under T1 and T2 treatments,while the growth of Maqiesu significantly decreased with the enhancement of UV-B radiation intensity.This result indicated that enhanced UV-B radiation could promote the growth of Sannianmang,but could inhibit the growth of Maqiesu.The contents of chlorophyll a,chlorophyll b,carotenoid and chlorophyll a+b in Sannianmang were not significantly different under T1 treatment from those under the CK treatment,but significantly increased under T2 treatment.When the UV-B radiation intensity was enhanced,leaf photosynthetic pigment content of Maqiesu decreased significantly.There was no significant difference in the chlorophyll a/b of Sannianmang and Maqiesu under different UV-B radiation intensities.Compared with CK,T1 treatment increased the net photosynthetic rate(Pn),stomatal conductance(Gs)and water use efficiency(WUE)of Sannianmang by 16.1%,25.0%and 7.9%,respectively,but there was no significant difference in photosynthetic characteristics between T2 treatment and CK.The Pn,Gs,Ciand Trof Maqiesu decreased with the enhancement of UV-B radiation intensity,but WUE firstly decreased and then increased with the enhancement of UV-B radiation intensity.There was no significant difference in the light response curve of Sannianmang under different UV-B radiation intensities,but the difference was significant in that of Maqiesu when photosynthetically active radiation(PAR)was higher than 200μmol·m^(-2)·s^(-1).The enhancement of UV-B radiation intensity decreased the Pnof Maqiesu under higher PAR.The initial fluorescence value(F0),maximal fluorescence value(Fm)and variable fluorescence value(Fv)of Sannianmang and Maqiesu significantly decreased with the enhancement of UV-B radiation intensity,and T2 treatment had the highest decline range.Under different UVB radiation intensities,there were no significant differences in the PSII maximum photochemical quantum yield(Fv/Fm)and PSII potential photochemical activity(Fv/F0)of Sannianmang,but the Fv/Fmand Fv/F0 of Maqiesu significantly decreased with the enhancement of UV-B radiation intensity.The ultrastructure of leaf cells was damaged in varying degrees under the enhanced UV-B radiation.Under T1 treatment,the epicuticular wax increased,stomata atrophied,chloroplasts tended to be oval,and more osmiophilic particles were accumulated in the leaves of two mango varieties,among them,the leaves of Maqiesu were partly broken,and a large number of black lipid droplets were formed in the cells.The arrangement of cell structure was disordered,the number of black lipid droplets significantly increased and the photosynthetic capacity decreased in the leaves of Maqiesu under T2 treatment.【Conclusion】Sannianmang with thicker leaf texture had higher tolerance to the enhanced UV-B radiation,while Maqiesu with thinner leaf texture was sensitive to the enhanced UV-B radiation.Therefore Sannianmang was more suitable for cultivation in the environment with stronger UV-B radiation than Maqiesu.