Ammonia oxidization is a critical step in the soil N cycle and can be affected by the fertilization regimes. Chinese milkvetch
(
Astragalus sinicus
L., MV) is a major green manure of rice (
Oryza sativa
L.) fields in southern China, which
is recommended as an important agronomic practice to improve soil fertility. Soil chemical properties, abundance and
community structures of ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) in a MV-rice rotation
field under different fertilization regimes were investigated. The field experiment included six treatments: control, without
MV and chemical fertilizer (CK); 100% chemical fertilizer (NPK); 18 000 kg MV ha-1 plus 100% chemical fertilizer
(NPKM1); 18 000 kg MV ha
-1 plus 40% chemical fertilizer (NPKM2); 18 000 kg MV ha
-1 alone (MV); and 18 000 kg
MV ha
-1 plus 40% chemical fertilizer plus straw (NPKMS). Results showed that NPKMS treatment could improve the soil
fertility greatly although the application of 60% chemical fertilizer. The abundance of AOB only in the MV treatment had
significant difference with the control; AOA were more abundant than AOB in all corresponding treatments. The NPKMS
treatment had the highest AOA abundance (1.19 × 10
8 amoA gene copies g
-1) and the lowest abundance was recorded in
the CK treatment (3.21 × 10
7 amoA gene copies g
-1). The abundance of AOA was significantly positively related to total N,
available N, NH4+-N, and NO3--N. The community structure of AOA exhibited little variation among different fertilization
regimes, whereas the community structure of AOB was highly responsive. Phylogenetic analysis showed that all AOB
sequences were affiliated with
Nitrosospira
or
Nitrosomonas
and all AOA denaturing gradient gel electrophoresis (DGGE)
bands belonged to the soil and sediment lineage. These findings could be fundamental to improve our understanding of
AOB and AOA in the N cycle in the paddy soil.
