| Global tropospheric ozone(O3)concentration has increased in recent decades due to the urbanization development.Surface ozone pollution is one of the environmental crisis that the mankind is facing increasingly serious and urgent need to solve.Under O3 stress,plants usually appear damage spot in leaves.And high O3 also accelerates leaf senescence,impairs the photosynthesis ability and other physiological and biochemical processes.Global climate change and extreme weather condition increase the interaction of O3 and other environmental factors.Trying to completely understand the responses of forest ecosystem under changing environment,particularly the responses of the urban ecosystem under O3 pollution,the research use to the main landscape greening tree species Pinus bungeana,Platycladus orientalis,Koelreuteria paniculata and Ginkgo biloba as the research object in Beijing,through the measurement of above-ground(Photosynthesis ability,physiological and biochemical trails)under different O3 oncentrations(normal environment atmospheric ozone concentration,normal environment atmospheric ozone concentration+40 nmol·mol-1,and normal environment atmospheric ozone concentration+80nmol·mol-1);according to the theoretical basis that the forest of ozone uptake and transpiration through the stomata coupling,different ozone concentration that forest absorb ozone test is artificial controlled,analysis of forest whole tree ozone uptake rate(FO3)of variation range and time for different ozone concentration,to confirm the relationship between ozone concentration and tree transpiration and ozone absorption;at the same time,and combination change characteristic of forest canopy stomatal conductance(Gc),to explore the relationship between forest absorption ozone and the environment,a clear understanding of how the ozone concentration influenced forest transpiration changes.This research serves the theoretical and practical basis for anti-air pollution and ecology improvement in the polluted city area.The results are as follows:(1)Under the condition of increasing ozone concentration,different tree species had the phenomenon of inhibiting the growth of trees.The height and diameter of trees increased slowly when ozone concentration increased,but there was no significant difference in the effect of ozone concentration on the diameter of different species.Under NF ozone concentration,the leaves of different tree species were intact,and the leaves showed no harmful symptoms.With the increase of ozone concentration,the leaves appeared yellow and dead,and the leaves wilted at the concentration of NF40 ozone.Under the ozone concentration of NF80,there were a lot of wilting,dead and deciduous leaves in the leaves,while Pinus bungeana and Platycladus orientalis had stronger ability to resist ozone pollution,while Koelreuteria paniculata and Ginkgo biloba had weaker ability to resist ozone pollution,and the increase of ozone concentration was more sensitive to the damage of broad-leaved trees.(2)With the increase of ozone concentration,stomatal density,stomatal opening and stomatal size of different plants decreased significantly,and there were significant differences among the stomatal characteristics of different tree species,the decrease rate of stomatal size of Ginkgo biloba was 1.14 and 1.12 times that of Pinus bungeana respectively,and the stomatal density of Pinus bungeana was higher than that of Ginkgo biloba.The stomatal density of Pinus bungeana was 360 per mm-2-510 per·mm-2,while that of Ginkgo biloba was 140 per·mm-2-196 per·mm-2,while the stomatal opening and size of conifer was smaller than that of broad-leaved tree,and the stomatal opening of Pinus bungeana was between 105?m2-180?m2.The stomatal opening of Ginkgo biloba was between 480?m2-695?m2 and 3.85-4.57 times of that of Pinus bungeana,the stomatal size of Pinus bungeana was 180 ?m 2?335 ? m2,the stomatal size of Ginkgo biloba was 820?m2-1200?m2,and the stomatal size of Ginkgo biloba was 3.42-3.58 times of that of Pinus bungeana.(3)The net photosynthetic rate,transpiration rate,stomatal conductance and water use efficiency of different tree species decreased significantly with the increase of ozone concentration,while the intercellular CO2 concentration of different species increased significantly with the increase of ozone concentration.The net photosynthetic rate,transpiration rate,stomatal conductance and intercellular CO2 concentration of Koelreuteria paniculata and Ginkgo biloba were higher than those of Pinus bungeana and Platycladus orientalis,and the water use efficiency of Pinus bungeana and Platycladus orientalis was higher than that of Koelreuteria paniculata and Ginkgo biloba.It is more obvious in broad-leaved trees.(4)The maximum photochemical efficiency(Fv/Fm),electron transport quantum yield,electron transfer rate(ETR)and chlorophyll content of different species decreased with the increase of ozone concentration,and the relative conductivity of different species increased with the increase of ozone concentration.The photochemical efficiency,electron transfer rate,chlorophyll content and relative conductivity of Pinus bungeana and Platycladus orientalis were higher than those of Koelreuteria paniculata and Ginkgo biloba under different ozone concentrations,and the effects of ozone concentration on plant physiological characteristics were more obvious in Koelreuteria paniculata and Ginkgo biloba.The results show that broad leaved trees are more sensitive to ozone.(5)The monthly and diurnal variation of liquid flow density of different tree species decreased with the increase of ozone concentration,and the water consumption and ozone absorption rate of different tree species decreased with the increase of ozone concentration.The water consumption and FO3 of the whole tree were higher than that of the coniferous tree under different ozone concentrations,and the water consumption and FO3 of the whole tree decreased significantly with the increase of ozone concentration,which was more obvious in the broadleaved trees.Under ozone concentration NF40 and NF80,compared with NF concentration,the water flow density of Koelreuteria paniculata and Ginkgo biloba decreased by 1.04 and 1.03 times of that of Pinus bungeana and Platycladus orientalis,and the water consumption of Koelreuteria paniculata and Ginkgo biloba was 1.82 and 1.56 times of that of Pinus bungeana and Platycladus orientalis,respectively.The decline rate of FO3 in Koelreuteria paniculata and Ginkgo biloba was 1.30 and 1.04 times of that of Pinus bungeana and Platycladus orientalis,respectively(6)In the growing season(May-October),the liquid flow density of different tree species in May was the highest,2.63 times of that of the smallest May.The variation of liquid flow density in different tree species in growing season was Koelreuteria paniculata(0.00087 g·cm-2·s-1)>Pinus bungeana(0.00052 g·cm-2·s-1)>Ginkgo biloba(0.00047 g·cm-2·s-1)>Platycladus orientalis(0.00013 g·cm-2·s-1).The daily variation of ozone concentration was in the range of 15?g·m-3-123.67?g·m-3.There was a positive correlation between ozone concentration and temperature,and the variation range of ozone canopy conductance was larger than that of FO3.The order of GO3 and FO3 of different tree species was Ginkgo biloba>Koelreuteria paniculata>Platycladus orientalis>Pinus bungeana in the whole year.The annual mean value of FO3 was 6.42±1.23 nmol·m-2·s-1 and GO3 was(9.10±2.14 mmol·m-2·s-1).The GO3 and FO3 of Koelreuteria paniculata and Ginkgo biloba were higher than that of Pinus bungeana and Platycladus orientalis.The positive correlations between GO3 and Ta and ozone concentration were 0.95 and 0.86,respectively.The decrease of GO3 with the increase of VPD and Ta,FO3 was increased with the increase of VPD and Ta.The effects of VPD and Ta on GO3 and FO3 of different tree species were different:Koelreuteria paniculata>Ginkgo biloba>Platycladus orientalis>Pinus bungeana.(7)The Koelreuteria paniculata and Ginkgo biloba were more sensitive to the increase of ozone concentration,but the Pinus bungeana and Platycladus orientalis were less sensitive to the ozone concentration,and with the increase of ozone concentration,the photosynthetic physiological characteristics,stomatal characteristics,water consumption and ozone absorptivity of coniferous trees were lower than those of broad-leaved trees.The results showed that coniferous trees had stronger ability to resist ozone pollution than broadleaved trees.Therefore,the species of coniferous trees,such as Pinus bungeana and Platycladus orientalis,and broadleaved trees should be selected as species with strong ozone resistance in the environment of serious ozone pollution in urban areas. |
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