Macronutrients, micronutrients, and growth factors

Carbon is rarely limiting for growth of photosynthetic species, but nitrogen and phosphorus often are.  Freshwater productivity is often limited by phosphate availability. Silicon is often limiting to diatom growth in nutrient-poor, oligotrophic lakes. Most other nutrients are present to excess in the aquatic environment.

Although some photosynthetic species are completely autotrophic, many require an external supply of vitamins, frequently thiamin, biotin, B12, and riboflavin, purines, pyrimidines, and other classes of growth factors. This requirement is termed auxotrophy, and it reflects the abundance of dissolved organic matter to be found in their environment, which allows the selection of populations that do not synthesize all their own metabolic requirements.