Nitrous oxide emission and denitrifier bacteria communities in calcareous soil as affected by drip irrigation with saline water

Abstract

Shortage of fresh water resources has become a fundamental and chronic problem for sustainable agriculture development in arid regions. Use of saline water irrigation has become an important means for alleviating fresh water scarcity. However, long-term irrigation with saline water may cause salt accumulation in the soil, and further affect nitrogen transformation and N2O emission. For this, we conducted a 10-year field experiment to evaluate the effect of irrigation water salinity and N amount on N2O emission and denitrifier bacteria communities. The experimental design was a 2 × 2 factorial with two irrigation water salinity levels (0.35 and 8.04 dS m−1, representing SF and SH) and two N amounts (0 and 360 kg N ha−1, representing N0 and N360). The results indicated that long-term saline water irrigation significantly increased soil salinity, moisture, and NH4-N content, while decreased soil pH, NO3-N, organic matter, and total nitrogen. Irrigation with saline water significantly inhibited N2O emission, that was associated with a level decreased by 45.19% (N0) and 43.50% (N360) compared with irrigation with fresh water. N2O emission increased as the N amount increased, the N2O emission was 161% higher in the N360 treatment than in the N0 treatment. In the unfertilized plots, saline water irrigation significantly reduced the activity of denitrifying enzymes, the abundance of nirK, nirS, and nosZ, as well as the diversity of denitrifying bacteria communities. In the fertilized plots, saline water irrigation did not significantly affect the abundance of nosZ, while significantly reduced the abundance of nirK and nirS. Saline water irrigation and nitrogen application altered the community structures of denitrifying bacteria with nirK, nirS, and nosZ, irrigation water salinity seemed to be having a greater impact on denitrifying bacteria community in comparison with fertilization. LEfSe analysis demonstrated denitrifying bacterial potential biomarkers increased as the water salinity increased, meaning that saline water irrigation could alter community structures of denitrifying bacteria, and promote the growth of dominant species. Our findings indicate that increased abundance of nosZ, nirK, and nirS would promote N2O emission, and although long-term saline water reduced soil N2O emission, it resulted in continuous increase of soil salinity.