Air Pollution's Impact: Crops And Trees At Risk

Air pollution has a detrimental effect on crops and trees. While trees can act as a natural barrier to air pollution, absorbing gaseous pollutants and intercepting particulate matter, they are also extremely sensitive to changes in air quality. High levels of air pollution can cause injury to crops and trees, reducing growth and yield and even leading to premature death.

The impact of air pollution on crops and trees depends on several factors, including the type and concentration of the pollutant, the length of exposure, the plant species, and the environmental conditions. Some common air pollutants that affect crops and trees include sulfur dioxide, nitrogen oxides, ozone, fluorides, and particulate matter.

The effects of air pollution on crops and trees can vary from visible markings on foliage to reduced growth, yield loss, and even death. Understanding and mitigating the impact of air pollution on crops and trees is crucial for maintaining the health and productivity of agricultural systems and natural ecosystems.

Ozone and other oxidants can cause necrotic lesions on leaves, or chlorosis (leaf yellowing)

Ozone is a highly reactive gas that can cause damage to plants, including crops and trees. One of the ways it does this is by causing necrotic lesions and chlorosis in leaves.

Ozone enters leaves through openings called stomata and oxidises (burns) plant tissue during respiration, damaging the leaves and reducing the plant's chance of survival. This process can cause necrotic lesions, which are medium to large, irregular dead areas on the foliage of mature leaves. The surrounding green tissue often turns yellow soon after symptoms appear, and defoliation rapidly follows. This can affect the quality of fruit.

Ozone can also cause chlorosis, a condition where leaves produce insufficient chlorophyll, which is responsible for the green colour of leaves. Chlorotic leaves are pale, yellow, or yellow-white. The affected plant may be unable to manufacture carbohydrates through photosynthesis and may die unless the cause of chlorophyll insufficiency is treated.

The effects of ozone on plants can be influenced by several factors, including soil moisture, the presence of other air pollutants, insects, diseases, and other environmental stresses. Different plant species also have varying levels of sensitivity to ozone.

Fluoride air pollution can cause marginal or tip necrosis on leaves

Typical fluorine injury symptoms on broadleaf plants include marginal and tip necrosis that spread inward. Conifer needles exhibit tip necrosis that spreads to the base. Marginal or tip necrosis on leaves is caused by fluoride accumulation in the plant tissues over long periods. Fluorides are first accumulated in the leaves and then are translocated towards the tips and margins of the leaves. The injury symptoms are produced only after a critical level of fluoride is attained. Fluoride air pollution can induce injury at very low atmospheric concentrations. The critical concentration for fluoride injury is 0.1 ppm for several days.

In conifer needles, common visible injury symptoms are chlorosis, later turning into red/brown discoloration, tip burn, and necrosis of the whole needle. Formation of sharply defined red/purple bands between healthy and injured tissue is also observed. In angiosperm leaves, common symptoms are zonation of necrotic areas, leaf cupping, curling of leaf edges, and ragged leaf margins. In sepals, petals, bracts, and awns, water-soaked margins and later tip and marginal necrosis are observed. Fluoride enters the leaf through the stomata and is moved to the margins, where it accumulates and causes tissue injury.

Particulate matter like cement dust can inhibit respiration and photosynthesis

Particulate matter, such as cement dust, can have detrimental effects on the respiration and photosynthesis of crops and trees. Respiration in plants is a vital process that involves the breakdown of organic molecules, such as glucose, in the presence of oxygen to release energy. This energy is then used for various cellular activities, including growth, repair, and photosynthesis. However, when particulate matter is introduced, it can lead to a coating on plant surfaces, including leaves—a major site of respiration. The tiny pores on the underside of leaves, called stomata, facilitate the exchange of gases during respiration. When these pores become blocked by particulate matter, the rate of respiration decreases, inhibiting the plant's ability to produce energy.

Cement dust, in particular, can have a significant impact on plants due to its composition. Cement is a fine powder that contains a mixture of minerals, including calcium, silicon, iron, and aluminum. When released into the air as dust, these particles can be easily inhaled by plants through their stomata. Once inside the plant, these particles can interfere with the plant's cellular processes, including respiration.

The effects of particulate matter on photosynthesis are also significant. Photosynthesis is the process by which plants convert light energy, carbon dioxide, and water into glucose and oxygen. It is the opposite of respiration, which breaks down glucose and oxygen to release energy. During photosynthesis, plants absorb light energy through their leaves. However, when particulate matter coats the leaves, it can block the pores and reduce the plant's ability to absorb light, thereby inhibiting photosynthesis.

Additionally, particulate matter can also affect the absorption of carbon dioxide, which is essential for photosynthesis. Cement dust, in particular, can form a layer on the leaves, reducing the rate of gas exchange. This disruption in carbon dioxide uptake can lead to a decrease in the plant's ability to produce glucose, which is a crucial source of energy for growth and development.

The impact of particulate matter on crops and trees can have far-reaching consequences. Reduced respiration and photosynthesis rates can lead to slower growth, decreased vitality, and even the death of plants. This, in turn, can affect the entire ecosystem, impacting other organisms that depend on these plants for food and habitat. Therefore, understanding the effects of particulate matter on plant respiration and photosynthesis is crucial for preserving the health of our environment and mitigating the detrimental effects of air pollution.

Sulphur dioxide can cause acute injury, with lesions on leaves

Sulphur dioxide (SO2) is a harmful pollutant that is released into the atmosphere primarily through the burning of fossil fuels by power plants and other industrial facilities. It can cause acute injury to crops and trees, leading to the development of lesions on their leaves. This occurs when plants absorb lethal quantities of SO2 through their stomata, resulting in the formation of sulphite and sulphate ions. The toxicity of these ions, particularly sulphite ions, damages the plant tissue and inhibits vital physiological processes, causing a range of adverse effects.

The accumulation of sulphite and sulphate ions in leaf tissue gives rise to two types of markings or symptoms: chronic and acute injuries. Chronic injury occurs when plants are exposed to low concentrations of SO2, typically below 100 parts per billion (ppb). Under these conditions, the rate of accumulation of ions is slow, and the cells gradually oxidize the sulphite ions, leading to a general chlorotic appearance of the leaves. This type of injury is characterized by mild chlorosis or yellowing of the leaf, with the lower surface turning silvery or bronzed without necrosis.

On the other hand, acute injury results from the absorption of lethal quantities of SO2. It manifests as marginal or intercostal areas of dead tissue, appearing as grey or green water-soaked areas. These areas eventually become bleached as they dry out, and the dead or necrotic regions may fall out, leaving a ragged appearance on the leaf. Severe injury can lead to the formation of an abscission layer at the base of the petiole, causing the leaves to fall off.

The sensitivity of plants to SO2 varies depending on the species and the duration and concentration of exposure. Some plants exhibit greater susceptibility to SO2, such as Chinese cabbage, which has been recorded to have a strong linear relationship between the rate of SO2 uptake and atmospheric concentrations. Prolonged exposure to SO2 levels greater than or equal to 0.1 µL L-1 resulted in a reduction in biomass and an increase in water-soluble non-protein thiols and total sulphur content in the shoots of Chinese cabbage.

The effects of SO2 on plant growth and development are complex and can vary depending on the plant species and the concentration and duration of exposure. Low concentrations of SO2 can stimulate the physiology and growth of plants, particularly those growing in sulphur-deficient soil. However, increased uptake of SO2 can lead to toxicity, inhibiting photosynthesis, impairing vital physiological processes, and reducing growth and productivity.

Nitrogen oxides can cause increased tree growth, making them more susceptible to damage

Nitrogen oxides can have a range of effects on trees. While they may be beneficial to vegetation in some cases, they can also cause damage. Nitrogen oxides can cause increased tree growth, but this can make trees more susceptible to damage.

Trees require a balance of nutrients to grow healthily. When exposed to higher levels of nitrogen, trees may put less resources into root growth. This can make them more vulnerable to environmental stressors such as drought, high winds, and pests.

In addition, nitrogen oxides can contribute to the formation of ozone in the lower atmosphere. Ozone is a harmful pollutant that can cause damage to trees and other vegetation. It can interfere with the normal processes of plants, including photosynthesis, and lead to reduced growth and yield.

The impact of nitrogen oxides on trees can vary depending on the species, age, and environmental conditions. It is important to consider the complex interactions between nitrogen oxides and other factors to fully understand their effects on tree growth and health.

To mitigate the negative impacts of nitrogen oxides on trees, it is crucial to reduce emissions from various sources, including power plants, agriculture, and vehicles. By controlling these emissions, we can help protect trees and maintain the health of our forests and natural ecosystems.

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