Lecture 4- Nitrogen Cycle SS221 pt1

N is used for what in a Plant

making chlorophyll, nucleic acids, enzymes, and energy transfer, building block of protien

N def symptoms

chlorosis stunted appearance think spindly stems

Nitrogen Pools (6)

Soil inorganic nitrogen, soil organic nitrogen, nitrate, Ammonium, Atmospheric N, Plant N

Nitrate

NO3- mobile, inorganic form, plant available form

Ammonium

NH4+ ammonium ion, inorganic form, plant available form, immobile

Soil Organic Nitrogen

largest pool of N in soil, only small amount mineralizes to a plant available form each year, part of actice,slow or passive soil OM pools

Ammonium NH4+ and Plant uptake

plant uses less energy to convert ammonia for synthesis of amino acids and proteins, moves primarily in soil by diffusion, uptake causes decrease in pH

Nitrate No3- and Plant uptake

plant reduces nitrate to ammonia first, most common source of N for crop plants, highly mobile in soil, increase in rhizopherese pH, moved by mass flow

Which form NH4+ or NO3- is needed

plants less than 3 weeks old do not have nitrate reductase enzyme so prefer NH4+, older plants show quicker visual response to NO3-

Mineralization

release of NH4+ during organic matter enzyme decomposition, enhanced in warm most well-

Conversion of Organic N to NH4+: Aminization

microbed break down proteins to amino acids

Conversion of Organic N to NH4+: Ammonification

mircobes convert amino acids to NH4+

N Immobilization

incorporation of inorganic N in microbial biomass to build cellular components, enhanced high C:N ratio

Nitrification

oxidation of NH4+ to NO3- by nitrifying chemoautotrophs, enhances by warm moist aerated soils

2 Steps of Nitrification

NH4+ (ammonium) → NO2- (nitrite) → NO3- (nitrate)

Biological N fixation

conversion of n gas in air to plant available N through microorganisms, symbiotic and free-libving bacteria and archaea diazotrophs