Nutrient Use and Remineralization

• Nutrients -> any element required by organisms for growth
• some nutrients are so abundant as to never limit growth
• in aquatic ecosystems limiting nutrients for primary producers is most often nitrogen, phosphorus, silicon, and iron
• lipids require phosphorus
• amino acids/proteins require nitrogen
• nucleotides require nitrogen and phosphorus
• primary producers use mostly inorganic nutrients
• animals and other eukaryotic organisms use organic nutrients
• bacteria use both inorganic and organic nutrients
• What are the two components of nutrient use?

  uptake and assimilation
• uptake -> process of nutrients being taken into cells from surrounding water
• assimilation -> incorporation of nutrients into organic molecules used for growth
• uptake can occur without assimilation
• the rate of uptake is dependent on concentration of nutrients in water
• rate of growth (assimilation) controlled by nutrient supply, pH, temperature, light
• nutrient concentration inside cell is more important than outside
• growth rate can be predicted by concentration of nutrients outside the cell
• Explain Luxury Consumption

  some organisms can take up nutrients at high rates when exposed to high nutrient concentrations for short periods, having nutrient storage is a competitive advantage. But organisms cannot sustain growth proportional to this uptake
• nutrient limitation -> control of growth or production by a nutrient or nutrients
• carbon, nitrogen, and phosphorus are typically most limiting in aquatic ecosystems based on demand relative to availability, however, for photosynthetic organisms CO2 is very abundant
• remineralization is release of inorganic nutrients by organisms
• What are the two processes that lead to remineralization?

  decomposition of dissolved and particulate organic matter and metabolic activity within living organisms
• how can primary producers lead to remineralization?

  cells leak and are broken releasing dissolved organic and inorganic nutrients
• How do heterotrophs lead to remineralization?

  excrete surplus nutrients as wastes
• for nutrients to be used there must be both uptake and assimilation
• uptake is controlled by concentration outside of cell
• assimilation is controlled by concentration inside the cell
• availability of nutrients is controlled by geology and land use
• remineralization is cycling of nutrients from organic to inorganic forms by organisms