Unformatted text preview: ium (NH3) and this is then used in synthesis of amino acids and then proteins. On Land Nitrogen fixation occurs in a symbiosis On Land Nitrogen fixation occurs in a symbiosis between some plants (in the pea family such as legumes) and bacteria in nodules associated with their roots • The added fixed nitrogen is a natural fertilizer for the plants Both of these multicellular cyanobacteria (Richelia and Trichodesmium) Both of these multicellular cyanobacteria (Richelia and Trichodesmium) are important in being able to add nitrogen to the marine ecosystem through N2 fixation. Why? Because often, dissolved N compounds such as ammonium (NH4) or nitrate (NO3) are present in concentrations so low, that their scarcity limits the growth of phytoplankton. • Through N2 fixation, these cyanobacteria can add more fixed N to the euphotic zone. On land we see enrichment of N depleted farmland when N2 fixers in soybean or clover plants grow in fields that lie fallow. Only prokaryotes are able to do this. N2 + 6H = 2NH3 Cyanobacteria are also important in N2 fixation in salt Cyanobacteria are also important in N
marshes and in coastal areas where they live on surface of sediments C...
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- Fall '08
- Darwin, Phytoplankton, euphotic zone