Advances in nitrification and nitrifying bacteria in grassland soil

Abstract: The research progress of nitrification and nitrifying bacteria in grassland soil were reviewed. Ammonium was converted to nitrate through the process known as nitrification. Nitrification is generally divided into autotrophic nitrification and heterotrophic nitrification. Autotrophic nitrification is performed by two physiologically distinct groups of Gramnegative chemoautotrophic bacteria belonging to the nitrobacteriaceae. The conversions of NH4+ to NO2- and of NO2- to NO3- were mediated by ammonium and nitrite oxidizing bacteria respectively. Urine returns by livestock grazing can result in addition of large quantities of urineN to soils. Urine patches could increase soil nitrifying activity and provide favorable conditions for the growth of nitrifying bacteria. Nitrification potential was significantly higher under legumes than under grasses. The impact of fire and soil pH on the nitrification has not yet draw an identical conclusion. Nitrification is an important way to produce N2O in addition to denitrification. Livestock grazing not only promote nitrification but also increase N2O emissions. With the intensive and specific research on grassland nitrification, the future directions on grassland ecosystem are suggested.