nitrogen cycle

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nitrogen cycle

movement of N-containing molecules between sources and sinks/reservoirs

N reservoirs

hold N for relatively short periods of time compared to C cycle (plants, soil, atmosphere)

atmosphere

main N reservoir- N in atm exists mostly as N2 gas, not usable by plants or animals

importance to plants and animals

all living things need N for DNA and amino acids to make proteins

nitrogen fixation

process of N2 gas being converted into biologically available (usable by plants) NH3 (ammonia) or NO3- (nitrate)

biotic fixation

certain bacteria that live in the soil, or in symbiotic relationship with plat root nodules convert N2 into ammonia (NH3)

abiotic fixation

lightning converts N2 gas into nitrate (NO3-) and FF combustion coverts N2 gas into ammonia (NH3)

cycle steps- assimilation

plants and animals taking in N and incorporating it into their biomass (plant roots take in NO3- or NH3 from soil, animals assimilate N by eating plants or other animals

cycle steps- ammonification

soil bacteria, microbes and decomposers converting waste and dead biomass back into NH3 and returning it to soil

nitrification

conversion of NH4 into nitrite (NO2-) and then nitrate (NO3) by soil bacteria

denitrification

conversion of soil N (NO3) into nitrous oxide (N2O) gas which returns to atmosphere

N2O (nitrous oxide)

greenhouse gas which warm earth’s climate, produced by denitrification of nitrate ion agricultural soils (especially when overwatered)

leaching and eutrophication

synthetic fertilizer use leads to nitrates (NO3) leaching- being carried out of soil by water