Plant Macro- and Micronutrient Minerals

All plants must obtain a number of inorganic mineral elements from their environment to ensure successful growth and development of both vegetative and reproductive tissues. These minerals serve numerous functions: as structural components in macromolecules, as cofactors in enzymatic reactions, as osmotic solutes needed tomaintain proper water potential, or as ionized species to provide charge balance in cellular compartments. Minerals can be divided into two classes, based on the relative amounts needed for plant growth (see Table 1). The macronutrients include nitrogen (N), potassium (K), calcium (Ca), magnesium (Mg), phosphorus (P) and sulfur (S); these are generally found in plants at concentrations greater than 0.1% of dry tissue weight. The currently recognized micronutrients include iron (Fe), zinc (Zn), manganese (Mn), copper (Cu), boron (B), chlorine (Cl), molybdenum (Mo) and nickel (Ni); these generally are found at concentrations less than 0.01% of dry tissue weight. These 14 minerals, along with the elements carbon (C), hydrogen (H) and oxygen (O), are broadly accepted as essential for the growth of all plants. Additional minerals, such as cobalt (Co), sodium (Na), silicon (Si), selenium (Se), iodine (I) and vanadium (V), have been shown to be essential or beneficial for certain plant species, but their widespread essentiality has yet to be established. Many other elements can be found in plants (over half the elements in the periodic table have been identified in some plant tissue), but these are thought to enter plants nonselectively. Most of these nonessential elements confer no known benefit to the plant, and many, such as cadmium (Cd) or chromium (Cr), are actually detrimental to plant growth.