Effect Of Highway Dust Pollution On Photosynthesis In Plant Leaves

Highway, as an important indicator of a nation's economic capabilities and development levels, has developed quickly with the rapid global economic progress. In the short span of the last decade, Chinese total mileage of highway has leapt up to the second place in the world, which has significant meaning to Chinese economic progress and the improvement of people's living standard. However, as a large exploitation and construction project, its negative impacts on ecological environment are especially prominent. So how to protect the ecological environment around highway has become a problem which is in dire need of solution.A large amount of dust could be unavoidable produced in highway construction processes, such as the building of roadbed and side slopes, road paving, and etc. The component of the dust in construction of highway is very complex, and it can be diffused widely. Dusting could cause damage not only to the normal metabolism, morphology, growth and development of vegetables, but even to plant communities. Up to now, there were little studies on the responses of the stomatal conductance (Gs), the net photosynthetic rate (Pn) and the transpiration rate (Tr) of plants' leaves to long term treatment of dust covering. Moreover, when choosing the greening plants, it is always only taken into account the plant's dust catching ability, but ignored the physiological change under dust covering would adversely affect the dust catching capacity of plant's leaves.In this research,the dusting stress in highway construction field was stimulated and the related physiological parameters after long term treatment of dust covering were examined in 20 sorts of plants which were chosen from native plants around the highway and the common greening plants. It was found that the net photosynthetic rate (Pn) and the transpiration rate (Tr) were both inhibited in most plants' leaves. Meanwhile the stomatal conductance (Gs) of leaves was reduced, too. The decrease in Pn by dusting in plants such as Ginkgo biloba, Pinus thunbergii Parlatore, Pittosporum tobira and Jasminum nudiflorum was mainly due to the inhibition of stomatas; but in plants as Forsythia viridissima Lindl, Berberis thunbergiicv. artropurpurea and Jasminum mesnyi, the decrease in Pn was mainly due to the inhibition of photosynthetic capacity in mesophyll cells. Moreover, we found the resistance abilities of frutex vegetables to dust covering stress were generally higher than that of arbor vegetables; plants such as Firmiana simplex, Platanus orientalis and Rhododendron simsii, which were not only good at dusting-catching but also resistant to dusting stress, could be applied as effective dust-catching plants. But sensitive plants to dusting stress, such as Ligustrun lucidum Ait, Platycladus orientalis and Koelreuteria bipinnata, should be chosen as greening plants only under certain conditions.Moreover, the inhibition effect on photosynthesis by mercury, which always adhered to dust particles, was also studied in this research. The results showed that along with the enhancement of applied mercury concentrations, the contents uptake by leaves increased while net photosynthetic rate (Pn) and leaf's apparent quantum yield (AQY) decreased. Moreover, mercuric chloride also decreased the photochemical efficiency (ΔF/Fm') of PS II under actinic light, electron transport rate (ETR) but increased non-photochemical quenching of chlorophyll fluorescence (NPQ). These results indicate that after mercuric chloride treatment the decline in net photosynthetic rates in leaves might mainly be due to the inhibition of photosynthetic electron transport.This study proposed integrative examination and evaluation of greening plants on the basis of combination the dusting-catching capacity with resistance ability to dusting stress of plants. Our results provided a scientific basis for selection and collocation of greening plants and a new way helping to choose the greening plant for dust catching.