Let s start by taking a look at the relative abundance of elements in organisms C, N, S, P, Mg, Fe, K, and Ca are the dominant elements in living organisms. One of the best early studies on plant nutrient requirements was published by a German chemist, Justus von Liebig in 1840. One of Liebig s ideas is called the Law of the Minimum , which states that the growth of a plant is limited by the element present in least supply. More recently, two classic studies expanded on this idea by suggesting that the body plans of organisms have relatively fixed element ratio requirements for growth. These have become known as the Redfield ratios .
Organisms require specific balances or ratios of nutrients.
This ratio happens to be characteristic of phytoplankton. By simply knowing how much carbon phytoplankton take up, you can predict how much nitrogen they will need to take up from the environment. By knowing the relative amounts of elements in the environment, you tell if certain elements are limiting growth. Here carbon is supplied in the environment above and beyond that required by phytoplankton. P ratio of about 7 for these species.