Soil 7 - N Cycling Flashcards
What are the two main processes in N cycling?
- mineralization (become inorganic N)
- Immobilization (become organic N)
What is the C”N Ration in an ideal microbial diet?
24:1
What is nitrification?
the biological oxidation of any reduced form of Nitrogen to a more oxidised form by autotrophic bacteria
Two steps:
NH4+ -> NO2- -> NO3-
(Nitrogen oxidation state lowers)
What are the 2 steps of nitrification?
- NH4+ to NO2 -
- NO2 - to NO3 -
What are the 5 main process in N cycling in soil?
- BNF N fixation
- mineralization and immobilization
- nitrification
- denitrification
- NH3 volatilization
What form of N do plants take up?
ammonium nitrate
- nitrate = very mobile in soil, while ammonium easily binds to soil and is unlikely to be lost to plants or water
Why do we want to prevent nitrification in agriculture?
to prevent oxidation of NH4+ into oxidised forms that are less available to plants (ex NO2-, NO3- which is prone to leaching or volatilizing)
How can we inhibit nitrification in agriculture?
paraffin-coated calcium carbide
- forms acetylene, which inhibits nitrifiers
What is denitrification?
- the major form of nitrate reduction in soil
- comes from using NO3 as an alternate electron acceptor
- many complex steps/side processes
- returns N2 to atmosphere
What is the only point where N2 returns to the atmosphere?
denitrification
What is an environmental control on denitrification?
- water (more denitrification)
- pore space (air) - (more nitrification)
- carbon source (more organic c = more denitrification???)
What are some impacts of nitrification/denitrification?
- economic (loss of fertilizer in agriculture)
- environmental (release of nitrous oxide, leaching of N into water)
How does biological fixation of N work?
conversion of N2 (triple bond) into usable organic forms
- complicated process with host-specific rhizobia
What are the steps to forming a N fixation symbiosis?
- plant roots release flavonoids to attract microbes
- bacteria release signal to plant
- root hair becomes root thread
- root nodule forms, produces nitrogenase
Under what conditions does nitrification occur?
oxic
How does the heterogeneity of soil influence denitrification?
- reaction hotspots/moments
- wet soils will have more denitrification
Under what conditions does denitrifcation occur?
- anoxic/low-oxygen
- when certain bacteria that produce nitrate reducctase are present (archaea that use copper/cadmium)
What is the hole-in-the-pipe conceptual model of N flux?
Nitrogen flux as a whole depend on rate of reactions (size of pipe) and size of holes in the pipe (based on environmental conditions)
What part of the N cycle is the NosZ gene associated with?
Denitrification
(N2O consumption and N2 production)
