Nitrogen and Sulfur Additions Improved the Diversity of nirK- and nirS-Type Denitrifying Bacterial Communities of Farmland Soil

SIMPLE SUMMARY: In this study, we investigated the effects of combined N and S additions on soil properties and N-cycling microorganisms. We found that soil treated with N and S additions had higher Shannon diversity and Chao 1 richness for the nirK- and nirS-related OTUs. We also found that, in the nirK-type denitrifying community, the addition of N and S promoted increases in the relative abundance of Bradyrhizobium, and in terms of the nirS-type denitrifying community, the N and S additions increased the relative abundance of Thiobacillus. Moreover, the N and S additions increased the activity of nitrate reductase and nitrite reductase. Most importantly, the nirK-type denitrifying community demonstrated a higher sensitivity to N and S additions. We expect that this research will be useful for the study of the nitrogen cycle in soil. ABSTRACT: Anthropogenic nitrogen (N) and sulfur (S) deposition can change above- and belowground biodiversity, including soil microbial diversity. The diversity of denitrifying microorganisms is of great significance to the calculation of the global nitrogen cycle and nitrogen flux. For a long time, nirK and nirS have been used as the functional genes to study denitrifying microorganisms, and have gradually become molecular markers for studying the composition and diversity of denitrifying bacteria. Here, three-time exposures to N and S applications (7, 30, and 60 days), were independently established. Additionally, the abundance, diversity, and structure of nirK- and nirS-type denitrifying communities were examined by sequencing analyses in response to three treatments, namely, N and S (T(N/S)), sodium chloride (T(NaCl)) and deionized water (pH = 7.0) (CK). Our results suggest that T(N/S) led to higher electrical conductivity (EC), total nitrogen (TN), total organic carbon (TOC), nitrate nitrogen (NO(3)(−)-N), ammonium nitrogen (NH(4)(+)-N), and lower pH compared with T(NaCl) and CK, which affected the diversity of nirK- and nirS-type denitrifying bacterial communities. We also observed that the nirK-type denitrifying community demonstrated a higher sensitivity to N and S additions. Overall, our results are important for the understanding of nitrogen in soil and N(2)O emissions.