All life on Earth requires certain essential minerals, such are iron and zinc, to function properly. Animals obtain these minerals from their diet, but plants have to take them up directly from the environment and that can create problems. This is because although these minerals are generally abundant in the soil and water, they are mainly present in the form of ionic species that are not very soluble and so can’t easily be absorbed by plant roots.
One solution to this problem adopted by many plants, as well as by bacteria and fungi that obtain minerals directly from the soil, is to release compounds known as siderophores that can bind these ionic species. Because the resultant complexes are much more soluble, they can easily be taken up by plants, providing them with the necessary minerals. An interesting adjunct to this binding process is that it tends to work more effectively with certain isotopes than others, producing a natural isotopic fractionation of the metal ions in soil and water. Read more.