ABSTRACT
Table 5.1 has listed the 19 elements that are generally found in all organisms. A handful of elements can be found in addition to the 19 listed at low concentrations; for instance, iodine and ªuorine, and a few trace elements have been found to be characteristic in just a few species: selenium, nickel, vanadium, chromium, and even the toxic element cadmium may substitute into enzymes that typically use zinc. In principle, each of the applied elements can be a limiting factor for growth, as discussed in
Section 2.2. A limiting element must of course be absolutely necessary for the considered organism and be present in a concentration that is lower than the other important elements relative to its use for building new biomass for the focal organism. e composition of the ecosphere reªects, however, the composition of the organisms, which means that the elements are o¬en present in a ratio close to the concentrations in Table 5.1. Furthermore, the composition of organisms is not an exact unchangeable value but rather a range. For instance, most plants can manage to grow with a phosphorus content of 0.4-2.0%. If the environment has a high phosphorus concentration relative to the need of the organisms, the organisms will accumulate more phosphorus, and if the phosphorus concentration of the environment is low, the plants are able to adapt to the conditions and cope with less phosphorus. is adaptability of the plants to the composition of the environment is reªected in the range of concentrations in the organisms and implies that a limiting concentration of an element is not a sharp exact value, but is a range that gradually, at lower concentrations, will limit the growth more and more. See also the discussion in Section 2.3.
