Reduction of Nitrate to Ammonium in Selected Paddy Soil of China
摘要
Three paddy soils soils were examined for their capacities of dissimilatory reduction of nitrate to ammonium (DRNA). ^15N-labelled KNO3 was added at the rate of 100mg N kg^-1 ,Either glucose or rice straw powder was incorporated at the rate of 1.0 or 2.0 mg C kg^-1 respectively,Three treatments were designed to keep the soil saturated with water: A) a 2-cm water layer on soil surface (with beaker mouth open);B) a 2-cm water layer and a 1-cm liquild paraffin layer(with beaker mouth open);and C)water saturated under O2-free Ar atmosphere.The soils were inculated at 28 ℃ for 5 days,There eas alomst no ^15N-labelled NH4^+-N detected in Treatment A.However,there was 1.4 to 3.4mg N kg^-1 ^15N-labelled NH4^+-n in Treatment B and 2.1 to 13.8 mg N kg^-1 in reatment C.Glucose was more effective than straw powder in ammonium production.Because there was sufficient amount of non-labelled NH4^+-N in the original soils. ^15N-labelled NH4^+-N produced as such should be the result of dissimilatory reduction.Studies on microbial population showed that there were plenty of bacteria responisble for DRNA process(DRNA bacteria) in the soils examined,indicating that number of DNRA bacteia was not a limiting factor ammonium prodction.However,DRNA bacteria were inferior in number to denitrifiers.DRNA process in soil suspension seemed to start after 5 days of incubation.Glycerol and sodium succinate,thought both are readily available carbon sources to organisms,did not facilitate DNRA process.DRNA occurred only when glucose was available and at the C/NO3^--N ratio of over 12 .It seemed that both availability and quality of the carbon sources affected DRNA.