Pollution in whatever form has negative impacts on the environment and the plants that reside in it. Pollution has many sources, from direct discharge of waste oil into waterways to air pollution from automobile exhaust. Some effects are short term and easily mitigated. Other effects are long term, with pollutants persisting in the environment or accumulating in plant tissues. Photosynthesis is an essential process within the ecosystem. Using sunlight, carbon dioxide and water, plants manufacture food and energy in a chemical process which occurs in plant leaves.
Ozone and Leaves
Gas exchange through the pores or stomata of leaves provides the necessary carbon dioxide for photosynthesis. However, a 1980 study published in Cellular and Molecular Life Sciences found that air pollution reduces the size of stomata, interfering with gas exchange. Insufficient carbon dioxide can slow or stop photosynthesis. This is further supported by a 2004 study which found that air pollution reduces crop yields.
Nonpoint Source Pollution
Nonpoint source pollution is pollution that comes from many diverse sources and enters the environment through surface water runoff. Agricultural runoff is the primary source of this type of pollution, according to the U.S. Environmental Protection Agency (EPA). Runoff introduces pesticides and fertilizers into waterways. Sometimes, the effect is immediate and plants die rapidly. High levels of phosphorus from fertilizers can cause algal blooms. Algal blooms set up a scenario where photosynthesis slows and finally stops as dissolved oxygen levels decrease in the water and turbid waters impede the flow of sunlight into aquatic environments.
Soil pollution impacts photosynthesis at the root level. Acidic rain caused by fossil fuel emissions increases the acidity of soils which causes a chemical to occur, creating toxic aluminum ions. These ions impede the plant's ability to take up nutrients, thereby slowing the process of photosynthesis and the overall growth of the plant.
Ground level ozone created by the greenhouse effect can create unfavorable conditions for photosynthesis to occur. Concentrations of greenhouse gases such as carbon dioxide prevent the release of radiant heat from the environment. Surface temperatures rise, increasing the rate of evaporation. Water becomes a limiting factor. To conserve precious resources, plants will close their stomata, reducing the availability of carbon dioxide to the plant. With limited carbon dioxide and water, photosynthesis slows.
Pollution can interfere with a plant's ability to undergo photosynthesis by physical damaging the leaves where it occurs. Ozone causes a condition called chlorosis, in which plants' leaves turn yellow from insufficient chlorophyll levels. Chlorophyll is vital for photosynthesis to occur. If levels drop, so too will photosynthesis. In high concentrations, pollution can kill off plant structures which will cause plants to cease food production in order to cope with environmental stresses.
- "Cellular and Molecular Life Sciences"; Effect of Air Pollution on the Leaf Epidermis at the Submicroscopic Level; K. K. Garg and C. K. Varshney; December 1980
- "Encyclopedia of Plant and Crop Science"; Air Pollutants: Effects of Ozone on Crop Yield and Quality; Hakan Pleijel; February 2004
- Elmhurst College: Acid Rain--Soil Interactions
- USDA Agricultural Research Service: Effects of Ozone Air Pollution on Plants
- U.S. Environmental Protection Agency: Protecting Water Quality from Agricultural Runoff
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