| Summary: | Using <i>Pinus bungeana</i>, <i>Platycladus orientalis</i>, <i>Koelreuteria paniculata</i> and <i>Ginkgo biloba</i> as research objects, three open-top chambers with different ozone-concentration gradients were set up (NF, NF40 and NF80) based on trunk sap-flow technology to study the difference in ozone absorption by trees under different ozone concentrations. The results showed that the monthly and diurnal variations of sap-flow density of different tree species decreased with the increase in ozone concentration, and the increase in ozone concentration reduced the water consumption, ozone uptake rate (<i>F</i><sub>O3</sub>), net photosynthetic rate (<i>P<sub>n</sub></i>) and water-use efficiency (WUE) of different tree species. The sap-flow density, water consumption, <i>F</i><sub>O3</sub> and WUE of <i>Koelreuteria paniculata</i> and <i>Ginkgo biloba</i> were higher than those of <i>Pinus bungeana</i> and <i>Platycladus orientali</i>s under different ozone concentrations. The sap-flow density, water consumption, <i>F</i><sub>O3</sub> and WUE of <i>Koelreuteria paniculata</i> and <i>Ginkgo biloba</i> decreased significantly at the ozone concentrations of NF40 and NF80; compared with the ozone concentration of NF, the sap flow density of <i>Koelreuteria paniculata</i> and <i>Ginkgo biloba</i> decreased by 1.04 and 1.03 times as much as that of <i>Pinus bungeana</i> and <i>Platycladus orientalis</i>, respectively; the water consumption of <i>Koelreuteria paniculata</i> and <i>Ginkgo biloba</i> decreased by 1.82 and 1.56 times that of <i>Pinus bungeana</i> and Platycladus orientalis, respectively; the decline rate of <i>F</i><sub>O3</sub> in <i>Koelreuteria paniculata</i> and <i>Ginkgo biloba</i> was 1.30 and 1.04 times that of <i>Pinus bungeana</i> and <i>Platycladus orientalis</i>, respectively; and the decline rate of WUE of <i>Koelreuteria paniculata</i> and <i>Ginkgo biloba</i> was 1.52 and 1.64 times that of <i>Pinus bungeana</i> and <i>Platycladus orientalis</i>, respectively. <i>Pinus bungeana</i> and <i>Platycladus orientalis</i> have stronger tolerance to ozone, while <i>Koelreuteria paniculata</i> and <i>Ginkgo biloba</i> were weak. A variety of conifers can be planted in areas with serious ozone pollution.
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