Plants as Bioindicators: the Soil pH Test
Some plants can tell us much about an ecosystem. These are bioindicators. Let’s see how reliable and universal they are.
Some plants and animals are hardy and can live in a range of environmental factors. Others have a limited range and are sensitive to changes in the environment. These are called bioindicators because they are among the first plants or animals to be affected when an environment changes.
For example, plants live and grow on nutrients from the soil. Many characteristics of the soil can affect the ability of their roots to extract nutrients. A key factor is the soil’s pH level.
Some plants can live in alkaline soils, some grow in acidic ones. If you see cloudberry (Rubus chamaemorus) and crowberry (Empetrum nigrum) plants (refer to the image), for examples, chances are the soil is very acidic: these species are usually found at peatlands with pH as low as 4.5. These plants are bioindicators of a soil’s low pH level.
People have long known that plants can tell us about the environmental characteristics of local soils, and botanists and farmers have compiled lists of plants that are specific to various levels of soil acidity. You can find lists of soil pH bioindicators for your region in books or on the Internet. By looking at the plant species on a plot of land, we can sometimes make a valid guess about the land’s pH level.
But are bioindicators universal around the globe? What if plants are adapting to local conditions and, as a result, changing their soil pH preferences? Together we can collect a significant amount of data from around the globe and check if we can rely on bioindicators.
What is pH?
pH stands for the power or potential of hydrogen. In simple terms, pH is a measure of the activity of hydrogen ions*. This activity can determine whether something is an acid or an alkaline (or base). pH levels in the soil can impact the availability of nutrients and, consequently, what can grow at a particular location. More information on soil can be found from this datasheet from the U.S. Department of Agriculture (USDA)
*Ions are when an atom or molecule loses or gains one or more electrons.