Effects Of Elevated O₃/CO₂on Photosynthetic And Growth In Two Species Of Urban Greenery

Urban is focus of industrial land. With the rapid development of industrialization, the concentration of O3and CO2was increasing rapidly, which had a great effect on photosynthetic physiological characteristics of plant species in the urban. Taking Osmanthus fragrans and Ilex rotunda Thunb as the research objects, using Open-top chambers for continuous separate and combined ventilation experiment with O3/CO2, we simulated composite effects on photosynthetic physiological function and growth of urban greenery as a result of increased atmospheric concentration of O3and CO2. In this ventilation experiment, set Ti (O3:100±10nmol·mol-1), T2(O3:200±10nmol-mol-1), T3(CO2:780±20μmol·mol-1), T4(CO2:1560±20μmol·mol-1), T5(O3:100±10nmol·mol-1; CO2:780±20μmol·mol-1), T6(03:200±10nmol·mol-1; CO2:1560±20μmol·mol-1), CK (natural O3and CO2concentration in chamber)7different concentrations of O3/CO2fumigation treations. The effects of different treatments on photosynthesis and growth of Osmanthus fragrans and Ilex rotunda Thunb were studied to analysis photosynthetic response mechanism of Osmanthus fragrans and Ilex rotunda Thunb to elevated O3and CO2concentration and predict the feasibility of Osmanthus fragrans and Ilex rotunda Thunb as composing plant species in the urban under future climate change. The main research results were as follows:(1) As the ozone concentration increasing, The net photosynthetic rates(Pn), stomatal conductance(GS), transpiration rate(Tr) and intercellular CO2concentration(Ci) significantly decreased both of the Osmanthus fragrans and Hex rotunda Thunb, the content of the chlorophyll and carotenoid decreased; the activity of PSII were restrainted, the actual photochemical efficiency(Yield) and relative electron transport rate(ETR) descreased; plant height and biomass reduced, the root to shoot ratio increased. Compared with the background of environmental atmospheric, The increased ozone concentration could cause a serious damage to Osmanthus fragrans and Ilex rotunda Thunb, through self-regulation to alleviate the damage as O3concentration increased to100nmol·mol-1; when O3concentration increased to200nmol·mol-1, resulting in the irreversible damage to photosynthetic of plants.(2) Elevated CO2concentration increased to780μmol·mol-1had significant enhanced the net photosynthetic rates (Pn) and intercellular CO2concentration(Ci) with the prolonged treatment days; the chlorophyll and carotenoid content are increased; The high CO2concentration promoted the activity of PSII, elevated the actual photochemistry efficiency and relative electron transport rate, for photosynthetic carbon assimilation to provide more ATP and NADPH, the heights and biomass were significantly increased, the root to shoot ratio decreased, while the shoot ratio decreased. Elevated CO2concentration increased to1560μmol·mol-1, During60d experiment, The net photosynthetic rates (Pn) and intercellular CO2concentration (Ci) significantly increased both of the Osmanthus fragrans and Ilex rotunda Thunb, the plant heights in T4enviroment grew better than in T3environment; at the time of75d treatment, the net photosynthetic rates (Pn) were lower than that of CK, the growth rate of the plant height had declined, the actual photochemistry efficiency reduction, it showed that Osmanthus fragrans and Ilex rotunda Thunb in elevated CO2concentration might have photosynthetic acclimation during long-term experiment.(3) In combination, the damage effects of elevated O3exposure on photosynthesis of Osmanthus fragrans and Ilex rotunda Thunb are alleviated by elevated CO2. Under T5treatment:The net photosynthetic rates (Pn) of Osmanthus fragrans is enhanced; the content of the chlorophyll and carotenoid have no significant change, the actual photochemical efficiency (Yield) and relative electron transport rate (ETR) also have no significant change; plant heights and biomass are higher than CK, Which indicates that780μmol·mol-1CO2have a greater effect on Osmanthus fragrans than100nmol·mol-1O3. The net photosynthetic rates (Pn) of Ilex rotunda Thunb is decreased; the content of the chlorophyll and carotenoid decreased; the activity of PSII were restrainted, the actual photochemical efficiency (Yield) and relative electron transport rate (ETR) descreased; plant height and biomass reduced, which indicates that negative effect of O3is more than positive effect of CO2on Osmanthus fragrans. Under T6treatment:The net photosynthetic rates and biomass of Osmanthus fragrans and Ilex rotunda Thunb are significantly lower than CK but higher than T2treatment, which indicated that1560μmol·mol-1CO2can largely relieve the damage of200nmol·mol-1O3.(4) Effect of elevated O3Photosynthetic characteristics and growth, Ilex rotunda Thunb are more sensitive to environment stress, Osmanthus fragrans resistance is stronger Ilex rotunda Thunb in environment stress. Therefore, under future climate change, Osmanthus fragrans resistance are more suitable as one urban greenery.