Response of Nitrifier and Denitrifier Abundance to Salinity Gradients in Agricultural Soils at the Yellow River Estuary

Abstract

Salinization is considered a threat to agricultural soil and decreases crop yield worldwide. Nitrification and denitrification are the core processes of soil N-cycle. However, the response of nitrifiers and denitrifiers to salinity in agricultural soils remains ambiguous. The study aimed to explore the effect of salinity on nitrifiers and denitrifiers communities in agricultural soils along a naturally occurring salinity gradient. The effects of salinity on the abundance, composition, and interactions of nitrifiers and denitrifiers in surface soils were investigated. The abundance of nitrifiers significantly decreased in response to the increase in salinity. Ammonia-oxidizing archaea (AOA) were more susceptible to salinity elevation than ammonia-oxidizing bacteria (AOB). Nitrospira and Nitrobacter showed a similar trend to the salinity gradient, but the relative abundance of Nitrobacter was increased in the saline soils. High salinity decreased the abundance of napA and nirK, but had no significant effect on other marker genes for denitrification. Besides electrical conductivity, total sulfur (TS)+available potassium (AK) and TN+TS+C/N+total phosphorus (TP)+AK significantly explained the variation in denitrifier and nitrifier communities. We also found that high salinity decreased the connections between different N functional genes. These results implied the alteration of the nitrogen cycling community by high salinity mainly through decreasing AOA, NOB, and some denitrifiers with nitrate or nitrite reduction potentials and weakening the connectivity between nitrogen cycling drivers.

Nitrogen Cycle in Farming Systems

“…The N min release rate is strongly dependent on both the biodegrability of N org and environmental factors affecting microbial activity. These issues are discussed in detail in this section [11][12][13].…”

“…Therefore, a question arises with respect to the extent to which this factor affects nitrification and denitrification, key components of the N cycle. This issue was studied in the soils of the Yellow River Estuary (China), evaluating the response of nitrifying and denitrifying microorganisms to a salinity gradient [13]. It was clearly found that increased salinity significantly reduced the abundance of nitrifiers.…”

Effect of the Sulfamethazine on Nitrogen Conversion in Alternate Wet and Dry Paddy Fields

“…AOA has been found to occupy higher abundances than AOB in many studies [51][52][53][54]. AOA and AOB respond differently to factors such as pH, salinity, NH 4 + , and NO 3 − [55]. AOA is better adapted to low NH 4 + concentrations, and it has higher abundance at higher NO 3 − concentrations, while AOB tends to have a higher abundance at higher NH 4…”