Image obtained from http://muextension.missouri.edu/xplor/waterq/wq0252.htm
- Nitrogen (N) is an
essential constituent of protein, DNA,
RNA, and chlorophyll.
- N is the most abundant gas in the atmosphere, but it must
be fixed or converted into a usable form.
Nitrogen Fixation Methods:
1) High energy fixation- a small amount of atmospheric
nitrogen is fixed by lightening. The high energy combines N and
H2O resulting in ammonia (NH3) and nitrates (NO3). These forms
are carried to Earth in precipitation.
2) Biological fixation: achieves 90% of the nitrogen
fixation. Atmospheric nitrogen (N2) is split and combined with
hydrogen (H) atoms to form ammonia (NH3).
Who performs nitrogen fixation?
- symbiotic bacteria (eg. Rhizobium spp.) living in association
with leguminous ( plants in the pea family), and root-noduled non-
leguminous plants (eg. Alnus spp.).
- free-living anaerobic bacteria
- blue-green algae (cyanobacteria)
Once NH3 is in the soil it combines with H+ ions
ammonium ion (NH4), or without it to form NO3. NH4+ and
NO3 are readily absorbed by plants.
[Sulfur Cycle ; Oxygen Cycle ;Phosphorus Cycle ;Carbon Cylce]