Plants' Resilience: Adapting To Air Pollution's Challenge

Plants are adapting to air pollution through changes in their genes. In Chicago, for example, biologists have observed genetic changes in weeds growing out of sidewalks. These changes may leave plants better suited to their environment, increasing their chances of survival and reproduction.

Plants have also been shown to adapt to air pollution through other means. Lichens and bryophytes, for instance, have undergone dramatic changes in urban and industrial areas. Some species of grasses and herbs have evolved tolerances to sulphur dioxide, and some sulphur dioxide-tolerant lichens have invaded inner-city areas.

Plants can adapt to air pollution by developing genetic changes that allow them to withstand the presence of toxins

Plants have a vast array of genes, and they use these to produce a large number of enzymes. In turn, these enzymes are used to produce complex chemical compounds, many of which are used for defence against insects and other animals. These defensive compounds are often called "specialized compounds". For example, plants in the mustard family make glucosinolate compounds, while many plants in the grass family produce benzoxazinoid compounds.

In some cases, plants have developed similar defensive compounds independently. For example, cyanogenic glucosides are present in unrelated plants like sorghum, cassava, and lima beans. These compounds produce cyanide, which is extremely harmful to animals, when activated.

In addition to these natural defences, humans have also intervened to develop genetically modified (GM) crops that are resistant to insects, viruses, and herbicides. For example, over 90% of the cotton planted in the USA, India, China, Australia, and South Africa contain GM toxin genes that protect them against certain insects.

By leveraging their genetic diversity and human intervention, plants can adapt to air pollution by developing genetic changes that enable them to withstand the presence of toxins.

Some plants have evolved to produce more of the enzyme superoxide dismutase, which helps them to deal with sulphur dioxide

Sulphur dioxide is a man-made air pollutant that has become increasingly concentrated in the atmosphere since the Industrial Revolution. Some plants have evolved to produce more of the enzyme superoxide dismutase, which helps them to deal with this pollutant.

Superoxide dismutase (SOD) is a family of metalloenzymes that catalyse the dismutation of superoxide radicals into molecular oxygen and hydrogen peroxide. In plants, there are three groups of SODs, depending on the prosthetic metals in their active sites: copper and zinc (Cu,Zn-SODs); manganese (Mn-SODs); and iron (Fe-SODs). These enzymes play a major role in combating oxygen radical-mediated toxicity.

Plants have responded to increasing concentrations of sulphur dioxide and other pollutants at the community, species, population, and individual levels. Recent studies in poplar and spinach strongly suggest that increased production of the enzyme superoxide dismutase may be a key factor in tolerating sulphur dioxide.

Superoxide dismutase has been found in all aerobic organisms examined, where it plays a major role in defending against toxic reduced oxygen species, which are generated as byproducts of many biological oxidations. The generation of oxygen radicals can be further exacerbated during environmental adversity, and consequently, SOD has been proposed as important for plant stress tolerance.

In summary, some plants have evolved to produce more of the enzyme superoxide dismutase, which helps them to deal with the man-made air pollutant sulphur dioxide by dismutating superoxide radicals into less harmful substances.

Plants can adapt by changing the structure of their leaves, such as by developing trichomes and ridges or grooves, which can help with the deposition of particulate matter

Plants can adapt to air pollution by changing the structure of their leaves. This includes developing trichomes and forming ridges or grooves on the surface of the leaves, which can help trap particulate matter.

Trichomes are small, hair-like structures that can be found on the surface of leaves. They can act as a physical barrier, preventing pollutants from entering the plant through the leaves. The thickness of the boundary layer of air surrounding the leaf depends on various factors, including the presence of leaf hairs or trichomes. By altering this boundary layer, plants can regulate the amount of pollutant that enters, thereby reducing the negative impact on their metabolic functions.

In addition to trichomes, leaves may also develop ridges or grooves, which can increase the surface area of the leaf and provide more sites for particulate deposition. This adaptation can help reduce the concentration of pollutants that directly come into contact with the leaf, thus lessening their toxic effects.

These structural changes to leaves can act as a defence mechanism, limiting the absorption of pollutants and increasing the plant's tolerance. While these adaptations may carry evolutionary costs, they can provide short-term survival advantages in polluted environments.

Furthermore, plants can also respond to air pollution by changing their physiological and biochemical processes. For example, they may produce reactive oxygen derivatives and increase the production of phenolic compounds, which can have both positive and negative impacts on plant-insect interactions.

Overall, the ability of plants to adapt to air pollution by altering leaf structure and function demonstrates their remarkable resilience in the face of human-induced environmental challenges.

Plants can also adapt by altering their leaf phenology, or the timing of leaf emergence and senescence, to avoid unfavourable conditions

Plants can adapt to air pollution by altering their leaf phenology, or the timing of leaf emergence and senescence, to avoid unfavorable conditions. This strategy can be particularly useful for mitigating air pollution during winter, when urban pollutant concentrations are often at their highest. By adjusting the timing of leaf growth, plants can remain productive during periods of lower pollution levels and reduce their exposure to harmful pollutants.

For example, some species may exhibit "reverse" leaf phenology, where leaf emergence occurs during the period when senescence would typically happen. This strategy can be effective in reducing air pollution damage to plants, as it allows them to avoid the peak pollution periods. Additionally, selecting plant species with longer in-leaf seasons can also enhance their ability to cope with pollution.

The choice of plant species with appropriate leaf phenology can be crucial for successful pollution mitigation. For instance, evergreen species that retain their leaves throughout the year can provide year-round benefits, while deciduous species that generally have longer in-leaf seasons can be preferable to those with brief in-leaf periods.

However, it is important to consider the trade-offs associated with different leaf phenologies. Evergreen species may be more susceptible to certain stressors, such as climate warming, than deciduous species. Additionally, the selection of plant species should take into account the specific environmental conditions of the planting site, including air pollution levels, temperature, and water availability.

Some plants have evolved to be more salt-tolerant, which can help them survive in areas with high levels of de-icing salt spray from roads

Plants have been adapting to urban pollution, traffic, and shrinking habitats through genetic changes. For example, weeds growing out of sidewalks in France have been found to produce compact seeds that drop close to the plant, allowing them to sprout in the surrounding soil.

Plants have also adapted to survive in areas with high levels of de-icing salt spray from roads. De-icing salts, such as sodium chloride (rock salt), are commonly used to melt ice and snow on roadways, driveways, and sidewalks. While these salts improve safety for motorists and pedestrians, they can cause damage to adjacent vegetation. Salt-laden water can spray onto plants from passing vehicles, causing foliage damage and increasing water stress for plants. In sensitive species, this can result in depressed growth and yield.

However, some plants have evolved to be more salt-tolerant, which helps them survive in areas with high levels of de-icing salt spray. Salt-tolerant plants can grow well in saline soils, and many herbaceous plants, such as grasses, adapt fairly readily to high salt levels. Woody plants also vary in their salt tolerance, with plants that have waxy foliage or scaled, protected buds generally being more tolerant of salt spray.

By understanding the impacts of salts on plants and implementing salt application management strategies, it is possible to protect plants or reduce plant injury due to salt exposure. Strategies such as reducing salt use, combining salt with other materials like sand or sawdust, and using non-sodium de-icing salts can help minimize the negative effects on vegetation. Additionally, physical barriers, such as burlap screens, can be erected to protect plants during the winter months.

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