Study On The Adaptability Of Transgenic Plants Of Viaduct Bridge In The Main Urban Area Of ​​Chengdu City Based On Light Environment

This study investigated the species resources, growth status and allocation of greening plants within broad range of Chengdu’s viaduct-shadow. It simulated the natural light environment under the bridge with Ecotect analysis software, in order to reveal the environment changes caused by natural light changes within broad range of viaduct-shadow, the paper observed the growth of selected greening plants, comparatively analyzed and explored the adaptability of greening plants, and gave some planting strategies according to the tectonic direction of viaducts, D value and the width of separation of the bridge joint.1) There are 32 species of greening plants planted under Chengdu’s viaduct bridges, including 13 kinds of herbs,16 kinds of shrubs, and 3 species of vine plants. There are 29 species of herbs and shrubs, which accounts for 90.6% of the whole speices, taking the biggest proportion. The most commonly planted herbs are Liriope spicata, Reineckea carnea and Iris tectorum. And the most planted shrubs are Pittosporum tobira, Fatsia japonica, Ligustrum sinense and Ligustrum X vicaryi.2) The tectonic trends of viaducts, the height to width ratio namely the D value and the separation of the bridge joint have a great influence on the light environment:about the North-South viaducts, the average sunshine hours during plants’ active growing period is better than East-West viaducts, the distribution of sunlight is uniform on both sides, and the most suitable area for plant is on the both edges with a width of 0-4m of the viaducts; about the East-West viaducts, the sunlight condition on the south side is obviously better than that on the north; but the average light condition of East-West viaducts is worse than that of North-South viaducts, namely the south sides under the East-West viaducts can achieve an average sunshine hourfor 8 hours.When the D value is less than 0.1, the clearance under the bridge is below 5m, and the average sunshine hours under the viaduct is less than 20%, but if the clearance under the bridge reaches 5m the average sunshine hours will grow to 20%; with the increase of the D value, the corresponding R value increased gradually, when the D value reaches 0.3, the corresponding R value change slowly; with the increase of D value, the viaduct North South low Rizhao area to "isosceles hill angle" as the basic type gradually disappear, the viaduct East-West low Rizhao area to "triangle" as the basic shape gradually disappear. The bridge body separation viaduct seam has a great influence on the bridge of Yin light environment, especially the East-West viaduct and bridge approach viaduct end low headroom area. When the bridge separating seam reached 3m, the natural light environment under the viaducts obviously improve.3) The relationship between the growth of greening plants under viaducts and the average sunshine hour distribution is as follow:when the bridge D value is less than 0.1 or the clearance under the bridge is less than 5m, the middle area within the viaduct is totally unsuitable for the growth of any plants, so it is economic to grow plants in the fringes of the viaduct; when the bridge D value is greater than 0.1 or the clearance under the bridge is higher than 5m, the natural light environment can basically meet the living of greening plants; about the North-South viaducts, the light condition in the north side is better than the south side, it is needed to grow shade tolerant plants in the south side, and about the East-West viaducts, there is little light condition difference between the east and west sides, so there is no special requirement on the shade tolerance of the species.The average sunshine hours distribution of natural light exert the greatest impact on the growth of greening plants when the headroom is low, namely the bridge D value is less than 0.1 or the clearance under the bridge is lower than 5m, and the average sunshine hours gained is less than 20%. The paper investigated the growth of greening plants under 31 viaduct bridges, So the adaptability of greening plants under viaduct bridges is as follow:Fatsia japonica>Ophiopogon japonicus>Pittosporum tobira.4) The paper divided the area within the viaduct into "suitable area" and "non-suitable area" and disscussed the utilization of green plants within the North-South and East-West viaduct based on the average sunshine hours. The paper found that the symmetrical arrangement mode should to taken when the viaduct is in a north-south direction, and it is needed to avoid the viaduct pier area at this situation; while it is better to plant light demanding plants in the South part of an East-West viaduct, and shade tolerant species on the north side; the bridge D value is greater than 0.1 or the clearance under the bridge is higher than 5m, it is better to choose light demanding plants.