Fig. 55-14c

1. Fig. 55-14c The Nitrogen Cycle N2 in atmosphere Assimilation Denitrifying bacteria NO3 – Nitrogen-fixing bacteria Decomposers Nitrifying bacteria Ammonification Nitrification NH3 NH4 NO2 – + Nitrogen-fixing soil bacteria Nitrifying bacteria

2. The Terrestrial Nitrogen Cycle • 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 (N2) is the atmosphere, 78% . N2 gas must be converted to other forms.

3. 4 processes of the Nitrogen Cycle • Nitrogen Fixation - process converts N2 into • NH4+ (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. Nitrification • NH4+ by ammonification, and NH4+ is decomposed to NO2- and often to NO3– by nitrification • Nitrifying bacteria convert NH4+ in soils • Plants absorb nitrates through roots Bashan, Y. and Levanony, H. (1987)

5. Ammonification • Breakdown of nitrogen compounds back into ammonia products NO3- → NH4+

6. Denitrification • Conversion of NH4+, NO2-, NO3- back to N2 gas (bacteria do this).