How do the ivy that can be seen everywhere under the viaduct "climb" up there?

Walking on the city streets lined with reinforced concrete, the air is filled with the smell of car exhaust and the burnt smell of the hot asphalt road. At this time, coming to an elevated bridge covered with ivy walls, it feels like being in the urban version of "The Wizard of Oz", bringing a touch of freshness and coolness.

Ivy wall under the viaduct

Source: Photo taken by the editor

What kind of plant is Parthenocissus fasciata? How does it grow vertically? Will it destroy the structure of an elevated bridge if it climbs all over the wall?

01

Ivy does not refer to just one type of plant

Although we always subconsciously think that this plant is called creeper when we see the green climbing all over the wall, in fact, creeper is a general term for various climbing plants . The most common and typical creeper belongs to the genus Parthenocissus, such as Parthenocissus, Parthenocissus quinquefolius, etc. The color of creepers mostly changes with the seasons. From September to October, creepers will gradually turn from green to red, adding a new look to the city. As a perennial large deciduous woody vine, creepers are highly adaptable and like humid environments, but they are not afraid of strong light, and are cold-resistant, drought-resistant, and barren-resistant. Especially in cities where green space is constantly being eroded, people widely introduce creepers into vertical greening practices.

Dijin (the leaves are single, growing on short branches, with three shallow lobes, green in spring and summer, and turn red or orange in autumn) Image source: idongde.com

Five-leafed brocade (the leaves are palm-shaped five-leaf compound leaves with narrow leaflets. The leaves are green in spring and summer and change to bright red in autumn)

Image source: idongde.com

02

How did the ivy climb up the viaduct?

In his essay "The Feet of Ivy", Mr. Ye Shengtao made a detailed observation and description of the feet of ivy from a literary perspective. The "feet" of ivy are actually suction cups, which are the main reason why ivy can cling to high walls. So, what is so magical about these suction cups? Let's explore the mystery from a scientific perspective!

The "legs" and "feet" of creepers

Image source: The Paper There are two reasons why creepers can firmly adhere to various wall surfaces. The first is the unique structural characteristics of the suction cup . Scientists observed the suction cup of creepers with the help of a scanning electron microscope and found that although the suction cup is only 1-3 mm in diameter, it has countless tiny holes similar to sponges and micro-tubes that extend in all directions . The sponge-like structure formed by these micro-tubes and micro-pores makes the adsorption power of creepers increase sharply.

Scanning electron microscope image of tendrils and immature suckers

Image source: Reference [1]

The suction cup not only makes its structure strong through "physical defense", but also increases the adsorption force through "chemical magic". During the growth process of the creeper climbing upward, the suction cup can secrete a kind of mucus from its internal micropores . Once the suction cup encounters the wall, a slow chemical reaction begins to occur, allowing the suction cup to firmly adhere to the wall. Therefore, when the suction cup contacts the wall, as the tip of the suction cup is continuously stimulated by contact, secretions are continuously produced, causing some air to be "wrapped" in the suction cup. During the growth process of the suction cup, the oxygen in the air "wrapped" in the suction cup will gradually be consumed, resulting in negative pressure in the suction cup , thereby increasing the adhesion between the suction cup and the wall.

Illustration of a creeping sucker that releases mucus to increase its sticking strength.

Image source: Reference [2]

It has been determined that a single sucker can withstand a weight that is 260 times its own weight during its growth and development, and the maximum tensile force it can bear is more than 2 million times its own weight. So don't underestimate those seemingly slender tendrils and suckers. If you don't use some strength, it's still difficult to pull them off.

03

Will ivy cause damage to the bridge?

You may have seen related reports in the news or on the Internet that "residential areas and old houses should regularly clean up creepers." So, why do we need to clean up creepers?

First, for some old buildings, the tiny cracks in the walls are just the right "carrying points" for creepers to climb. The tentacles of creepers penetrate into the cracks in the walls, which will expand the cracks . The acidic substances secreted by the creepers' suction cups will also cause a certain degree of corrosion to the walls , making old buildings more likely to collapse when encountering natural disasters such as earthquakes.

Source: Shangguan News Secondly, the spread of creepers will also affect the quality of life and comfort of residents. In summer, a large number of mosquitoes will gather around creepers, increasing the possibility of mosquito bites and disease transmission. Houses surrounded by creepers will affect lighting and heat transmission, causing the rooms to be cold and damp. In addition, a large amount of creepers will cause certain public safety hazards. In the winter season of water shortage, the leaves on the creepers will temporarily wither, and the withered leaves will become natural "fuel". Once a fire occurs, the creepers will become the "guide" of the flames. Therefore, in communities where creepers are rampant, the creepers in the community will be cleaned up regularly to avoid fires.

Image source: Infinite Leshan

It seems that ivy is harmful to buildings, so why do we always see ivy under urban viaducts? First of all, most viaducts use reinforced concrete as the main structural material. The bridge body itself has a strong corrosion resistance, and the size of the gaps on the surface of the bridge body can generally be ignored . Therefore, the adsorption and corrosion of ivy have a very small impact on the viaduct. Furthermore, since the viaduct exists in the urban traffic space, ivy has almost no impact on the quality of life of residents. Therefore, introducing ivy under urban viaducts is actually a way of "taking the essence and removing the dregs", which realizes the risk avoidance of ivy and maximizes the advantages.

04

What are the benefits of planting creepers under viaducts?

First of all, creepers can alleviate the urban heat island effect (referring to the "high temperature" of cities caused by a large amount of artificial heating, high heat storage bodies such as buildings and roads, and the reduction of green space). The urban heat island effect is gradually intensifying, causing the city temperature to rise and turn into a "furnace". By planting creepers in suitable areas, the green coverage area of ​​the concrete surface can be significantly increased at the lowest cost, effectively alleviating the urban heat island effect and making the city cooler.

Image source: Photo Network

Secondly, the creeper can protect the bridge . The creeper is not only a parasol, but also an umbrella. When it rains, the rain first hits the leaves of the creeper, and the leaves filter and buffer the rain. In this way, the intensity of the viaduct being wetted and washed away by rain will be greatly reduced.

Finally, creepers can effectively beautify the urban environment . Compared with other plants, creepers have strong climbing ability and can climb directly from the bottom of the bridge to the deck of the viaduct, effectively increasing the amount of green in the city. The strong adaptability and resistance of creepers make it grow well and flourish without a lot of manual management and maintenance. In addition, in large cities, viaducts are filled with a lot of car exhaust and noise. Planting creepers under viaducts can also purify the air and reduce noise.

Source: Photo taken by the editor

Therefore, for viaducts, the planting and growth of creepers has more advantages than disadvantages. When it is difficult to expand the green area of ​​our city plane, choosing vertical greening planting not only increases the beauty and wildness of the city, but also improves the ecological quality of the city. Why not?

References

[1]He Tianxian. Study on the adhesion of Parthenocissus tricuspidata suction cups[D]. South China University of Technology, 2012.

[2]S. Xi, F. Tian, ​​G. Wei, X. He, Y. Shang, Y. Ju, W. Li, Q. Lu, Q. Wang, Reversible Dendritic-Crystal-Reinforced Polymer Gel for Bioinspired Adaptable Adhesive. Adv. Mater. 2021, 33, 2103174.

[3] Tian Fulin, Li Hong, Liu Chengyan, Wang Zhijia, Cheng Guangrong, Zhao Haibo. Analysis of sucker secretions of Parthenocissus tricuspidata by gas chromatography-mass spectrometry and high performance liquid chromatography-tandem time-of-flight mass spectrometry [J]. Physical and Chemical Testing (Chemical Section), 2013, 49(10): 1219-1222+1227.

Author: Cao Yang, PhD in Ecology, Lecturer at Henan Agricultural University Planner & Editor: Rain