NUTRIENT CYCLES
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Transcript NUTRIENT CYCLES
Nitrogen and Phosphorus Cycles
Martha E. Rosemeyer
IES
January 29, 2003
One of three dynamic processes
of ecosystems
Energy flow
Nutrient cycles
Succession
Energy flows from the sun to entropy
through a functioning food web
Two types of nutrient cycles
Volatile
atmospheric reservior
N, S
Non-volatile
No atmospheric reservior
P, K, Ca, Mg all micronutrients
Nitrogen cycle
N2O
N2
2
Nitrification
3
Gliessman,
1998
modified
N Pool Size (Stocks) are
relatively big
Atmosphere
g N 1021
Terrestrial biomass g N 1015
Soil organic matter
g N 1015
Flows small
Rate limiting steps with respect to
getting N into terrestrial system:
Via lightning (very small)
Via Biological N Fixation
natural
legume crops
Via Industrial fixation of fertilizer
Via Fossil fuel burning
What is biological nitrogen fixation
(BNF)?
Second most important biochemical
reaction of ecosystem after photosynthesis
to life on earth
Involves the reduction of N from molecular
state N2 to NH3 in which form it can be
incorporated into an organic (C containing)
molecular structure
Involves microbes
BNF
Regardless of organism uses nitrogenase
enzyme for to fix N2 to ammonia NH3
NH3 + org. acids amino acids proteins
White clover, Trifolium repens
“Trebol blanco”
Temperate zone green manure crop
seed
Human-caused NF = or greater
Natural terrestrial BNF
BNF from crops
40 x 1012 g N fixed/yr
Fertilizer industry
80
Fossil fuel burning
20
Total human-caused
144
BNF terrestrial ecosystems 100
Microbes: The Ancient Ones
Responsible for all major processes on
earth, including decomposition and
photosynthesis and nutrient cycling
Major cycles of Earth could continue
without plants and animals
Most microbes are beneficial!
Most bacteria 99% cannot be cultured
Therefore we know little about them!
A ton of microscopic bacteria may
be active in each acre of soil.
Bacteria dot the surface of strands
of fungal hyphae.
--Soil Biology Primer
Life on earth: starting with
microbes
First N fixed by lightning and meteor
impact
Formation of first amino acids and protein
N-fixation early because N-limited
environment in water
Terrestrial system: P limited environment
Mycorrhizal fungi have allowed plants to
become terrestrial
Nitrogen cycle:mediated by microbes
= Microbial mediation
2
3
Gliessman 1998
modified
P Cycle
P is an important plant nutrient, anion
Released from soil, taken up by plants and
released to soil
Green Rev ag is totally dependent on P rock
P rock is basically a valuable, nonrenewable resource for agriculture
some deposits contaminated with Cd, Pb, As
10% of the P which is applied to land is
flushed way causing eutrophication of lakes
Dead zone in Gulf of Mexico due
to nutrients from Mississippi
The phosphorus cycle
= Microbial mediation
mycorrhizae
Gliessman 1998
P cycle
Brady, 1999
Roots of Common Bean (Phaseolus vulgaris)
from Costa Rica
Mycorrhizal fungus
stained blue
Non mycorrhizal
Components of association
fungus + root = mycor + rhiza
They are the rule, not the exception:
Most of world’s vascular plants have
association, except Brassicaceae (cabbage
family) and a few other plant families
Fungus: takes up water and P, receives CHO
from plant
Enables plants to live in low P, low water
environments
Mycorrhizae aid soil aggregation
Mycorrhizal fungi link root cells to soil particles. In this
photo, sand grains are bound to a root by hyphae from
endophytes (fungi similar to mycorrhizae), and by
polysaccharides secreted by the plant and the fungi.
Credit: Jerry Barrow, USDA-ARS Jornada Experimental Range,
Las Cruces, NM.
Closing nutrient cycles
Making the cycle circular
The nutrient comes back to the “stock” or
“pool” that it started with-- none is lost
In a human time frame
This is an important component of
sustainability
Chinese have used “night soil” for
centuries to close nutrient cycle