probably very ancient. As Liebig's law of the minimum notes, the essential element present in the smallest amount (called limiting factor) is the one that determines the growth rate of a population. Iron is the most common limiting element in phytoplankton communities and has a key role in structuring and determining their abundance. It is particularly important in the high-nutrient, low-chlorophyll regions, where the presence of micronutrients is mandatory for the total primary production. See also Chemosynthesis Lithotroph RISE project Expedition that discovered high temperature vent communities Notes References 1. Katrina Edwards. Microbiology of a Sediment Pond and the Underlying Young, Cold, Hydrologically Active Ridge Flank. Woods Hole Oceanographic Institution. 2. Coupled Photochemical and Enzymatic Mn(II) Oxidation Pathways of a Planktonic Roseobacter-Like Bacterium Colleen M. Hansel and Chris A. Francis* Department of Geological and Environmental Sciences, Stanford University, Stanford, California 94305-2115 Received 28 September 2005/ Accepted 17 February 2006 Biology terminology Trophic ecology Microbial growth and nutrition Planktology