1. Litter N loss. Physical: leaching can remove 0-20% (?) of N pool. Biological: net process Fungi and bacteria take up N from the soil solution to “prime” breakdown of high C:N litter ( net immobilization ). Net loss of N occurs when relative availability of C is low (so low C:N).
1. Litter N loss
Twigs and stems
% initial mass remaining
% (initial mass remaining)
% initial N remaining
% (initial N remaining)
Mack and D’Antonio 2003
Microbes have to spend protein (exoenzymes)
to get protein!
Microbes only mineralize N when they are starved for C!
Microbial C:N = 10:1
Microbial growth efficiency = 40% of C can be used for
Growth (@ C:N of 10:1) and 60% is respired as CO2
immobilize N from soil sol’n
microbes break even
microbes mineralize N
Substrate C:N = 50
Substrate C:N = 25
Substrate C:N = 15
Microbial growth efficiency differs
Gross NH4+ mineralization = Total amount of NH4+ mineralized regardless of fate
Gross NH4+ immobilization = Total amount of NH4+ taken up by microbes
Net NH4+ mineralization = Net accumulation of N in soil solution that is presumably available for plant uptake; N in excess of microbial demand
Net NH4+ immobilization = Net reduction of N in soil solution
What determines the fate of NH4+?
What determines the fate of NO3-?