1. Fig. 55-14c Decomposers N 2 in atmosphere Nitrification Nitrifying bacteria Nitrifying bacteria Denitrifying bacteria Assimilation NH 3 NH 4 NO 2 NO 3 + – – Ammonification Nitrogen-fixing soil bacteria Nitrogen-fixing bacteria

2. The pathway in which nitrogen moves through the ecosystem Nitrogen is a component of amino acids, proteins, nucleic acids (DNA), ATP The main reservoir of nitrogen (N 2 ) is the atmosphere, 78%. N 2 gas must be converted to other forms. The Terrestrial Nitrogen Cycle

3. 4 processes of the Nitrogen Cycle Nitrogen Fixation - process converts N 2 into NH 4 + (ammonium ions). Done by nitrogen fixing bacteria found in soil or nodules on roots of legumes Examples of legumes: peas, beans, alfalfa, peanuts, clover

4. NH 4 + by ammonification, and NH 4 + is decomposed to NO 2 - and often to NO 3 – by nitrification Nitrifying bacteria convert NH 4 + in soils Plants absorb nitrates through roots Bashan, Y. and Levanony, H. (1987)

5. Ammonification Breakdown of nitrogen compounds back into ammonia products

6. Denitrification Conversion of NH 4 +, NO 2 -, NO 3 - back to N 2 gas (bacteria do this).