Differentiated responses of nirS- and nirK-type denitrifiers to 30 years of combined inorganic and organic fertilization in a paddy soil

Abstract

ABSTRACT The responses of soil denitrifiers to inorganic and organic mixed fertilization in paddies have not been well evaluated. The abundance and diversity of nirS- and nirK-type denitrifiers in paddies after 30-year fertilization were estimated using quantitative PCR and Illumina MiSeq sequencing. The nirS gene abundance was two orders of magnitude higher than the nirK gene and both were reduced by fertilization. The high manure addition (NPK + 60% OM) decreased nirK gene abundance by 32.7% compared to inorganic fertilization alone (NPK) and decreased its community Chao1 index by 30.2% compared to unfertilized control (CK). Fertilization significantly changed the proportion of dominant (mean proportion > 1%) operational taxonomic units (OTUs) of both denitrifiers. Fertilization increased the proportion of OTUs belonged to cluster III (48.7–97.3%) of the nirS-type denitrifiers compared to CK. NPK + 60% OM increased that belonged to cluster II (48.0%) compared to the low manure addition (NPK + 30% OM). Total nitrogen and organic carbon correlated significantly with the abundance, diversity and community structure of the nirK-type denitrifiers, while they solely correlated with the nirS-type denitrifier community structure. Our results demonstrate that abundance and diversity of the nirK-type denitrifiers are more, while the community structure is less, sensitive to inorganic and organic mixed fertilization than the nirS-type in paddy soils.