What are counterion effects? I was reading the following article on wikipedia about Hydroponics

Unlike most nutrients, plants can tolerate a high concentration of the
$\ce{SO4^2−}$, selectively absorbing the nutrient as needed.
Undesirable counterion effects still apply however.

Can somebody explain me what is meant by counterion effects? Is it just the presence of the counterion, i.e. the concentration of the counterion in solution?
Here is a passage from Marschner P. (2012). Marschner’s mineral nutrition of higher plants. 3rd Edn. London: Academic Press:



In the context of the wikipedia table, it means that while you can have a high concentration of sulfate, you should consider the cation of the substance (e.g. calcium sulfate, potassium sulfate, ammonium sulfate) as well when trying to figure out the effects on a plant.