Biogeochemical Cycling – Fall 2010

Theme

Modern Changes in the Nitrogen Cycle

Friday Discussion GroupDiscussion Leader: Priya Ganguli12 November, 2010

• N 5th most abundant element in solar system• Essential for synthesis of nucleic acids and proteins• For every 100 atoms of C in cells, need 2 to 20 atoms of N• Biogeochemistry of N primarily oxidation-reduction and microbially mediated• Secondarily influenced by long-term cycling through geosphere• N2 largely unavailable to organisms• NO3

- and HN4+ (fixed forms) often limit primary productivity in both marine &

terrestrial ecosystems

Nitrogen Fixation

prokaryotes in bacterial and

archaeal domains

reduce N2 gas to ammonium

ion (NH4+)

from Baker MA, Dahm CN, Valett HM, 2000

elec

tron

acc

epto

rs

nitrate (NO3-)

reduction coupled to anaerobic

oxidation of Corg

N2 gas(denitrification)

or

NH4+

(dissimilatory nitrate reduction to ammonium)

(DNRA)