Download A. Nitrogen fixation

Biogeochemical Cycles
24 of 103 elements are required by organisms:
Six are Macronutrients: C,H,N,O,P,S
Other 18 are Micronutrients
BIOGEOCHEMICAL CYCLES
The complete pathway that a chemical macronutrient element takes through the
biosphere, hydrosphere, atmosphere and lithosphere.
I. Active and Storage Pools
Elements are transferred between compartments (pools):
Active Pools: accessible to living things
Storage Pools: inaccessible
II. CARBON CYCLE
Carbon cycles between biosphere and atmosphere in respiration, photosynthesis
and combustion.
Carbon cycle diagram
Play the carbon cycle simulation game in class.
III. Nitrogen Cycle
78% of atmosphere is N2
But it is not in a form usable by most organisms
Nitrogen fixation: conversion of nitrogen to usable form
Nitrogen Cycle
A. Nitrogen fixation
1. Biological
a) by photosynthetic bacteria & algae
b) by legumes
2. Industrial
a) by manufacture of N fertilizer
b) combustion of fossil fuels
Biological fixation
a) Free-living N-fixing bacteria and algae
-autotrophic
-fix nitrogen
b) Bacteria that are symbiotic
with legumes; infect
root nodules
Legume crops: clover, alfalfa, soybeans, peas, beans, peanuts
Industrial fixation
a) manufacture of N fertilizer
b) Combustion of fossil fuels; forest fires
B. Denitrification : Denitrifying bacteria convert usable N back to N2 in atmosphere.
Outgassing : Release of N to atmosphere during volcanic eruptions.
Currently, Industrial fixation > Biological fixation :
N fertilizer
Combustion of fossil fuels
Cultivation of legumes
-Result is excess nitrogen in biosphere, which runs into streams and oceans;
stimulating growth of algae and depleting oxygen