|MadSci Network: Environment & Ecology|
Reena, The answer to your question is yes and no. Land plants such as trees are affected by acid rain in two main ways. The increase in acidity changes the soil chemistry so that plants are less able to absorb minerals (such as magnesium). The increase in soil acidity also can kill a type of fungus that lives around the roots of many plants (called mycorrhizae). These fungi live in a mutualistic relationship, that is, they have a kind of symbiosis in which both the plant and the fungus benefit. The plant may benefit from the fungi's better ability to absorb nutrients of the fungus may help the plant in resistance to insects. So, losing mycorrhizae can leave plants vulnerable to insects and both loss of the fungus and increased soil acidity can cause plants to starve for minerals. As for algae, these organisms are similar to land plants because increased acidity changes their ability to obtain certain minerals. They are quite different, though, in the main way that acid rain affects algae. All photosynthetic organisms require carbon dioxide. Land plants get it from the atmosphere. Aquatic plants get it from the water and acidity affects both the amount and chemical form of the oxidized carbon present. When CO2 dissolves in water it forms carbonic acid which dissociates into carbon dioxide (CO2), bicarbonate ion and carbonate ion. How much of each ion is present depends on pH or acidity. At low pHs which indicate acid conditions, most of the carbon is in the form of CO2. This is the only form that can be used directly for photosynthesis. (The other forms can be used by many algae, but must be converted to CO2 before entering the carbon synthesis cycle in the cell). In addition to changing the carbon into the CO2 form, it also decreases the total amount of CO2 that can dissolve in the water. So the result is that the carbon is available in the right form, but there is less of it. Less carbon means less photosynthesis and that means less growth. So in an acid lake, you would probably find less total amount of algae. Since all algae can use straight CO2, you would likely find a lot of diversity at least until the lake becomes very acid, then you would find only acidophilic (or "acid loving") algae. By the way, acid rain has little effect on marine algae. That is because seawater contains and can hold far more dissolved CO2 and carbonates. The carbonates act as a chemical buffer against changes in pH.
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