Element Required By Higher Plants
Table shows the list of sixteen elements that fulfil the criteria of essentiality stated above, their approximate adequate concentration and approximate number of atoms required with molybdenum (Mo) serving as the reference point. Look at the difference! The requirement of hydrogen atoms is about 60 million times the number of Mo atoms. It is because H is an essential part of thousands of chemical compounds with which the plant is made of, whereas Mo is required only in one or two enzyme mediated reactions. Scientists have added a few more elements to the list of sixteen though they have found them essential only for certain group of plants.
These are, sodium (Na), cobalt (Co), silicon (Si), nickel (Ni) and even chromium (Cr), tin (Sn) and fluorine (F). Some specific organisms may require other elements. For example, certain algae apparently also require the elements vanadium (Va), silicon (Si) or iodine (I), while some ferns utilise aluminium (Al) and some local weeds absorb and accumulate selenium (Se) in high amounts.
Table: The essential element required by higher plants