Subject: Effect of acid rain on plants

What is acid rain, and what are the effects on plants, and what sorts of experiments might I conduct to test them?

This is a very general question and I'm not certain my answer will help you with your experiments. The effects can be boiled down to two things:

1) physiological damage to plant cells/plant tissues

2) geochemical shifts in soils and soil waters that impede growth by affecting absorption of nutrients by roots and/or by leaching nutrients from soil.

1 affects different plants differently and certain tissues of the plants are more susceptible than others. Young rootlets and leaf shoots are typically very sensitive to low pH conditions but other aspects of the plant can be harmed as well.2 affects the composition and makeup of soil water, which is a main source of nutrients for the plant and soil substrates themselves. Excess acid in soils can dissolve soil substrate, leading to erosion, cause de-adsorption and migration out of the growth zone of important trace metals and nutrients (especially ammonium ions) and release to solution of toxic quantities of other metals (such as Fe). The effects depend upon the normal mineralogic and organic makeup of the particular soil, as well as other factors such as rainfall amounts and slope of the growing surface. It is difficult to go from generalizations such as these to specific plants because each plant will respond differently. Some are adapted to be more tolerant to changes in environment (including natural variability in pH).I am not a biologist so I'm afraid I can't give you any more specific info for individual plants.

You could try running experiments to test both of these parameters. Use at least two types of plants, two types of soils, your local rain water, and rain that has been acidified to a pH of 3 to 3.5. I would use an atomizer (spray bottle) to water various plant types planted into both soil types with both regular and "acid" rain to test number 1 above. I would test number two above by treating soils with regular and acid rain daily for a week, and then planting plants in to the soils and watering with regular rain only (this way, you can distinguish affects on the soil itself from effects on the plants roots).

Please be very careful when making your acid rain. Always add acid to water (not vice versa), wear safety goggles and gloves, and plan ahead for accidental spills. You should need a very small amount of nitric or sulfuric acid. I suggest you get this from a chemistry teacher at your school and ask for his or her supervision in making the acid rain.

Dr Ken Rubin, Associate Professor
Department of Geology and Geophysics
University of Hawaii, Honolulu HI 96822

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