Effect Of Elevated Atmospheric O₃ On Aboveground And Underground Biological Processes Of Two Genotypes

In recent years, atmospheric ozone is continuously increasing, which has caused great economic loss of agricultural production in China. Most previous stdies focus on the effects of ozone stress on aboveground parts of plant, but neglect the effects on soil ecosystem, especially the response of rhizosphere microorganisms to O3 stress. Moreover, the linking between aboveground and underground parts of plant is less concerned. In fact, these informations are important for evaluting effects of O3 stress on agricultural production. In present study, O3-sensitive (S156) and 03-tolerant (R123) plant were used to investigate effects of O3 stress on aboveground and underground parts of plant and their linking with and withought arbuscular mycorrhiza in speicially-designed growth chamber that simulated elevated atmospheric ozone. In addition, response of AM fungi to elevated O3 was also observed. The main results are as follows:(1) O3 stress caused leaf injury in R123 and S156 plants. Relative to non-mycorrhizal plant, AM inoculation delayed injury manifestation and decreased injury index in leaf of R123 plant, but only injury manifestation was delayed in S156 plant. In S156 plant, chlorophyll concentrations (Chl a, Chl b and carotenoid) were decreased by elevated 03, while they were increased by AM inoculation. However, opposite trend was found in R123 plant in the treatments of O3 stress and AM inoculation.(2) O3 stress decreased photosynthesis rate (Ps), stomatal conductance (Condi), the maximum quantum efficiency of PSⅡ(Fv/Fm), electron transportation rate (ETR), photochemical quenching (qP) and transpiration (Trmmol), and increased intercellular CO2 concentration (Ci), minimum fluorescence (Fo) and maximum fluorescence (Fm). These changes indicated O3 stress produced inhibition for plant physiological process. AM inocation increased Ps, Condi, Fv/Fm, ETR, qP and Trmmol, and decreased Ci, Fo and Fm, indicating AM inoculation alleviated inhibition produced by deviated O3. However, there were diffierence between two genotypes.(3) Experiment on 13C isotope showed that 70nl/L O3 resulted in higherδ13C in root, stem and leaf of R123 plant, but lowerδ13C in root, stem and leaf of S156 compared to ambient O3. AM inoculation did not alter response ofδ13C in R123 plant, but changedδ13C in S156 plant.(4) Microbial community structure in rhizosphere of two gentypes was significantly altered by O3 stress and AM inoculation, but they were slightly affected in hyphosphere. Microbial community structure in rhizosphere of S156 showed greater response to O3 stress than that in rhizosphere of R123 plant. This indicated that there was linking between physiological process and rhizosphere microorganisms under O3 stress.(5) O3 stress decreased mycorrhizal colonization rate and external hypha in two genotypes, and resulted in higher spores in rhizosphere. O3 stress significantly increased total glomalin content in rhizosphere and hyphosphere of two genotypes, but slightly affected easily extractable glomalin content. In addition, there was no significant difference between two genotypes.