Physiological Responses of Two Lolium Varieties to the Enhancements of Tropospheric O_3 Concentration

The variations of the physiological indexes of annual Lolium multiflorum and perennial Lolium perenne leaves under different O_3 concentrations(80,120,160 nmol ·mol~(-1))were investigated using open top chambers(OTCs).The results showed that two Lolium varieties had the similar injury symptoms induced by O_3 stress,while brown injury spots appeared on Lolium multiflorum earlier.Elevating O_3 concentration,the content of malondialdehyde(MDA) significantly increased by 21.7%and 28.1%;the activities of superoxide dismutase(SOD) increased by 71.2%and 129.8%;peroxidase(POD) increased by32.3%and 57%,whereas net photosynthetic rate(Pn) decreased by 51.6%and 57.5%;stomatal conductance(G_s) decreased by 45%and 52.5%;maximum photochemical efficiency(F_v/F_m) decreased by6.4%and 5.5%and the actual photochemical efficiency(Φ_(PSII)) decreased by 18.9%and 10.5%in the leaves of two Lolium varieties,respectively.Therefore,Lolium perenne is more insensitive to the high concentrations of O_3 than Lolium multiflorum,because the stomatal regulation and antioxidant capacity of Lolium perenne are stronger.This study provides a scientific basis and reference for screening ozone resistant grasses under global climate change.