Cl rarely deficient in nature but it is essential in plant nutrition.  It is found in the soil as anion and plays two roles in plant nutrition: Cl is integral to the process in which water is split, thus releasing H+ ions and O2 gas Cl is a mobile anion within the plant where is functions in osmoregulation affecting cellular expansion and stomatal opening and closing. It also functions as a counter-balance to cations to maintain charge neutrality.