nitrogen cycle & nitrogen fixation
TRANSCRIPT
NITROGEN CYCLE
&NITROGEN FIXATION
Done bySaquib ahmed
NITROGEN CYCLE
Nitrogen cycle is a natural cyclic process in which it becomes a part of the living organisms, before it is sent back to the atmosphere.
The nitrogen cycle represents one of the most important nutrient cycles found in terrestrial ecosystems. Nitrogen is used by living organisms to produce a number of complex organic molecules like amino acids, proteins, and nucleic acids.
AMMONIFICATION Ammonification or Mineralization is
performed by bacteria to convert the ammonia to ammonium. Nitrification can then occur to convert the ammonium to nitrite and nitrate
This process liberates a lot of energy which can be used by the saprotrophic microbes
NITRIFICATION Nitrification is the process by which ammonia
is converted to nitrites and then nitrates. This process naturally occurs in the environment, where it is carried out by specialized bacteria.
This energy is the only source of energy for these prokaryotes
They are chemoautotrophs Chemoautotroph is an organism, typically a
bacterium, which derives energy from the oxidation of inorganic compounds.
Prokaryote is a microscopic single-celled organism which has neither a distinct nucleus with a membrane nor other specialized organs.
NITROGEN FROM ATMOSPHERE
Out gassin
g
Atmospheric fixation
Root uptake
Nitrate NO3-
Plant protein
Soil organic nitrogen
Atmospheric Nitrogen
Biological fixation
ATMOSPHERIC NITROGEN FIXATION Electrical storms Lightning provides sufficient
energy to split the nitrogen atoms of nitrogen gas,
Forming oxides of nitrogen NO and NO2
ATMOSPHERIC POLLUTION This also happens inside the internal
combustion engines of cars The exhaust emissions of cars contribute a
lot to atmospheric pollution in the form of NOx
These compounds form photochemical smog
They are green house gases They dissolve in rain to contribute to acid
rain in the form of nitric acid The rain falling on soil and running into rivers They contribute to the eutrophication of
water bodies Nox are oxides of nitrogen, especially as
atmospheric pollutants
CONCLUSION Adding nitrate fertiliser clearly helps the
growth of plants The presence of microbes permits the peas to
grow much better. The peas grow better in the presence of the
microbes than they do with nitrate fertiliser added
The difference is due to the present of mutualistic nitrogen fixing bacteria which live in the pea roots.
Mutualism is the way two organisms of different species exist in a relationship in which each individual benefits. Similar interactions within a species are known as co-operation.
THE NITROGEN FIXERS Cyan bacteria are nitrogen fixers that
also fix carbon (these are photosynthetic).
Rhizobium bacteria are mutualistic with certain plant species e.g. Legumes.
They grow in root nodules. Azotobacter are bacteria associated
with the rooting zone (the rhizosphere) of plants in grasslands.
Alafalfa (Medicago sativa)
THE HUMAN IMPACT
Nitrate NO3-
Atmospheric fixation
Out gassin
g
Plant protein
Atmospheric Nitrogen
Ammonium NH4
+
Soil organic nitrogen
Biological fixation
MAKING THINGS BETTER
The need for synthetic fertilisers can be reduced by cultural practices
Avoiding the use of soluble fertilisers in soil prevents leaching
Rotating crops permits the soil to recover from nitrogen hungry crops (e.g. wheat)
Adding a nitrogen fixing crop into the rotation cycle
Ploughing aerates the soil and reduces denitrification
Draining water logged soil also helps reduce denitrification
