Plants' Superpowers: Can Air Pollution Be Their Kryptonite?

Plants are the basis for the functioning of terrestrial and aquatic ecosystems, and they are often used to filter particulate matter pollution from the air. However, plants are not immune to the harmful effects of air pollution. Air pollution can have both direct and indirect effects on plants, impacting their growth, physiology, and ability to function within their ecosystems. This paragraph will explore the effects of air pollution on plants and discuss whether their abilities are decreased by air pollution.

Air pollution affects soil chemistry, limiting nutrient availability for plants

Plants are often regarded as nature's saviours, mitigating the impacts of pollution in the environment and making the air cleaner and safer for human beings. However, plants too have their limits and are affected by pollutants to varying degrees. Air pollution can significantly affect the quality of soil, and in turn, limit the availability of nutrients for plants.

Soil is a cornerstone of life on Earth, providing homes for most organisms and many of the nutrients, minerals, and elements that are essential for growth and biological functions. When air pollution occurs, the precipitation that falls onto the soil becomes acidic. This acid precipitation alters the chemistry of the soil, affecting plant growth and the quality of water bodies that the soil feeds into. As soils become more acidic, their ability to retain many essential nutrients, minerals, and elements decreases.

For example, as the pH of the soil increases, plants may suffer from insufficient iron intake, leading to iron chlorosis. This condition causes leaves to turn yellow with dark green veins, and over time, the leaves may turn white. Similarly, particulate matter deposited onto the soil from air pollution can change the soil's pH, affecting the ability of plants to utilise nutrients. For instance, alkaline dust increases soil pH, changing its chemistry and limiting the plant's ability to utilise nutrients.

Furthermore, air pollutants that are deposited on the soil, such as heavy metals, first affect the functioning of roots and interfere with the plant's ability to capture resources from the soil. These reductions in resource capture, including mineral nutrient uptake and water uptake from the soil, will negatively impact plant growth through changes in resource allocation to the various plant structures. Thus, air pollution can indirectly affect plant health and growth by altering the chemistry of the soil and limiting the availability of essential nutrients.

Pollutants like ozone and CO2 can induce oxidative stress in plants

Plants are incredibly helpful in mitigating the impacts of pollution in the environment, making the air safer and cleaner. However, they too have their limits and are affected by pollutants to varying degrees. One of the negative effects of air pollution on plants is the induction of oxidative stress by pollutants like ozone (O3) and carbon dioxide (CO2).

Ozone is a secondary pollutant formed from the interaction between oxygen (O2), nitrogen oxides (NO and NO2), and volatile organic compounds (VOC) in the presence of UV radiation. Ozone is a highly phytotoxic compound, and its concentration in the troposphere has increased significantly between the 19th century and the 2000s. While the annual average concentration is leveling off in the USA and Europe, it continues to rise in Asia. Acute concentration peaks over short periods can cause plant damage.

Elevated ozone concentrations increase oxidative stress in vegetation and threaten the stability of crop production. Studies have shown that elevated ozone levels reduce photosynthetic carbon gain in various plant species, including maize, sugarcane, and switchgrass. This reduction in photosynthesis leads to decreased yields, with current ozone pollution in the United States estimated to decrease maize yields by up to 10%.

Carbon dioxide (CO2) is also an air pollutant that can induce oxidative stress in plants. While CO2 is essential for photosynthesis, its excess or limitation can cause stress. For example, when plants are subjected to ozone pollution, they tend to close their stomata to prevent the entry of ozone, which negatively affects the entry of CO2. This decrease in CO2 causes a slowing of biochemical reactions, impacting the plant's overall health.

Additionally, high levels of ozone and CO2 can cause oxidative stress in the chloroplast and apoplast of plants, leading to cell damage and death. This stress can be mitigated by the plant's antioxidant systems, which utilize molecules like ascorbate and glutathione to detoxify reactive oxygen species (ROS). However, if the stress exceeds the plant's defensive capacities, it may lead to plant death.

Air pollution can cause irreversible damage to plants, such as cell death and leaf necrosis

Plants are often regarded as nature's saviours, mitigating the impacts of pollution in the environment and making the air cleaner and safer for human beings. However, plants have their limits and are affected by pollutants to varying degrees. Air pollution can cause irreversible damage to plants, such as cell death and leaf necrosis.

Air pollutants like particulate matter, when deposited on leaf surfaces, can clog stomatal openings. This deposition may change the leaves' light absorption and reflection of photosynthetically active radiation (PAR). As a result, the plant's secondary stresses are exacerbated, and physiological processes, like photosynthetic rate, are affected, disturbing the usual metabolism. Increased NO2 concentrations lead to inflated accumulation of nitrites and cellular acidification, resulting in negative responses, including ROS generation, inhibition of N-assimilation, and acute leaf damage, which can cause leaf necrosis and even plant death.

Ozone (O3) is another air pollutant that can cause irreversible damage to plants. O3 is a highly reactive molecule and one of the most powerful oxidizing agents known. It moves through the boundary layer of the leaf and is then absorbed by the plant tissue through the stomata. O3 initiates alterations and detoxification and repair responses in the plant. However, the exposure can lead to visible injury symptoms on leaves, such as white spots that turn into brown necrotic spots, indicating leaf necrosis.

Additionally, exposure to NO2 affects the leaf chlorophyll content and causes oxidative damage to plants. While antioxidants play a critical role in protecting plants from this damage, if the plant's antioxidant levels are below the 'ROS-neutralizing capacity', it can result in oxidation of biomolecules, damage to proteins, and even activation of apoptosis.

Air pollution can also affect plants indirectly through soil pollution. Pollutants like heavy metals can first contaminate the soil and then be taken up by plant roots, interfering with soil resource capture and plant growth. Soil pH changes due to pollution can also affect the availability of nutrients to plants, leading to insufficient nutrient intake and, eventually, plant death.

Plants' abilities to remove pollutants vary depending on foliage and leaf characteristics

Plants are often used to filter particulate matter pollution from the air, especially in cities. However, plants are also susceptible to harm from air pollution. The ability of plants to remove pollutants depends on various factors, including the plant species, the type and size of pollutant particles, and the characteristics of the foliage and leaves.

The electromagnetic charge of the leaf surface, influenced by the plant taxa, plays a role in attracting and capturing particles. The leaf surface can also influence the deposition of pollutants through its friction and shear properties. In addition, the size and density of stomata, which are tiny openings on the leaf surface, can impact the entry of pollutants into the leaf. Some pollutants enter through the stomata, while others may be captured on the leaf surface or enter through the leaf cuticle.

The morphology of leaves, including their size, shape, and complexity, can also affect their ability to capture and remove pollutants. Smaller leaves with higher complexity, such as ridges or grooves, are generally more effective at removing super-micrometre particles. On the other hand, stomatal characteristics become more critical for the uptake of sub-micrometre particles and gaseous pollutants.

Evergreen species, with their longer foliage longevity, are generally more advantageous for air pollution mitigation since they provide a more extended period for pollutant deposition. Additionally, the presence of trichomes (fine outgrowths) on leaves can be beneficial for capturing certain types of particles.

The selection of plant species for air pollution remediation should consider the specific pollutants present and the environmental conditions. Some plants may be more suitable for indoor environments, while others are better suited for outdoor use. By evaluating the characteristics of foliage and leaves, we can identify plant species that are well-adapted to removing specific pollutants and create effective vegetation barriers to improve air quality.

Air pollution can alter the physiological processes of plants, impacting growth patterns

Plants are often regarded as nature's air purifiers, playing a crucial role in maintaining the cleanliness of the air we breathe. However, the narrative changes when we consider the impact of air pollution on plants themselves. Air pollution can alter the physiological processes of plants, influencing their growth patterns and overall health. This intricate relationship between air pollution and plant life warrants further exploration to understand the delicate balance of our ecosystem.

Air pollution, a pervasive issue stemming from various sectors such as industry, commerce, and transportation, casts a wide net of harm that extends beyond humans and animals. Plants, too, fall victim to the detrimental effects of pollutants. Air pollutants, including sulfur dioxide, ozone, and nitrogen oxides, can wreak havoc on the intricate physiological processes that govern plant growth and development.

One of the key ways air pollution impacts plants is by interfering with their photosynthetic systems. Ozone (O3), for instance, inhibits the export of sucrose, leading to a buildup of carbohydrates and starch in the leaves. This disruption results in reduced photosynthesis, hindering the plant's ability to convert sunlight into energy for growth. Consequently, there is a decrease in the availability of photosynthetate, which is essential for the plant's growth and development.

Additionally, air pollution can alter leaf longevity and patterns of carbon allocation within plants. The presence of pollutants can cause damage to leaf cuticles and affect stomatal conductance, further impeding the plant's ability to photosynthesize effectively. These direct effects on the photosynthetic systems can have cascading consequences for the overall health and growth of plants.

Moreover, air pollution can indirectly affect plants by modifying their environment. Pollutants can change the pH levels of the soil, making it too acidic or alkaline. This alteration in soil chemistry disrupts the availability of nutrients to plants. For instance, a pH higher than 7.5 can lead to an insufficient intake of iron, resulting in a condition called iron chlorosis. This deficiency manifests as yellow leaves with dark green veins, ultimately impacting the plant's growth and vitality.

In conclusion, air pollution has the potential to significantly alter the physiological processes of plants, thereby impacting their growth patterns. From direct effects on photosynthetic systems to indirect modifications of the soil environment, the intricate relationship between air pollution and plant life is a critical area of study. Understanding these impacts is essential for preserving the delicate balance of our ecosystem and devising strategies to mitigate the harmful effects of air pollution on plant life.

Frequently asked questions