中国某些水稻土中硝态氮向铵态氮的还原研究

Three paddy soils were examined for their capacities of dissimilatory reduction of nitrate to ammonium (DRNA). 15N-labelled KNO3 was added at the rate of 100 mg N/kg. Either glucose or rice straw powder was incorporated at the rate of 1.0 or 2.0 mg C/kg respectively. Three treatments were designed to keep the soil saturated with water: (1) a 2-cm water layer on soil surface (with beaker mouth open); (2) a 2-cm water layer and a 1-cm liquid paraffin layer (with beaker mouth open); and (3) water saturated under an O2-free Ar atmosphere. The soils were incubated at 28℃ for 5 days. There was almost no 15N-labelled NH4+-N detected in Treatment 1. However, there was 1.4 to 3.4 mg N/kg 15N-labelled NH4+-N in Treatment 2, and 2.1 to 13.8 mg N/kg in Treatment 3. 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 responsible for DRNA process (DRNA bacteria) in the soils examined, indicating that number of DRNA bacteria was not a limiting factor for ammonium production. However, DRNA bacteria were inferior in number to denitrifiers. The DRNA process in soil suspension started after 5 days of incubation. Glycerol and sodium succinate, though both are readily available carbon sources to organisms, did not facilitate DRNA process. DRNA occurred only when glucose was available and at a C:NO3--N ratio >12. Both availability and quality of the carbon sources affected DRNA.

Reduction of nitrate to ammonium in selected paddy soils of China