Changes in denitrifier communities and denitrification rates in an acidifying soil induced by excessive N fertilization

Abstract

ABSTRACT A long-term experiment was conducted in soils across a decreasing pH gradient (7.0, 6.3, 5.7, 4.9 and 4.3). Intact soil cores across the pH gradient were sampled and incubation experiments were used to measure denitrification capacity (DC) and denitrification potential (DP). The size and structure of denitrifier communities were determined via real-time PCR and high-throughput sequencing techniques, respectively. The results revealed that soil pH was significantly and positively related to DP, DC, abundances and diversities of denitrifying genes. The nirS-harboring denitrifiers were favorable in soil pH > 5.7, whereas nirK-harboring denitrifiers played a major role in strongly acid condition (pH < 5.7). Phylogenetic lineages of nirK and nosZ rather than nirS communities were selected by soil pH and some specific ecotypes dominated at strongly acid soils. Soil pH was the only significant factor shaping the composition of nirS gene. Besides pH, total carbon, total nitrogen and NO3 –N were critical factors changing composition of nirK and nosZ genes. Overall, in strongly acid soils, the low-pH-adapted nirK and nosZ genotypes play crucial roles in N2O emission from denitrification and effective soil carbon and nitrogen managements could regulate N2O emission by shaping the composition of nirK and nosZ genes.