Nitrifiers and nitrification in extremely saline soils

Ammonia oxidation reaction driven by ammonia oxidizing archaea ammonia oxidizing bacteria and nitrite oxidation reaction driven by nitrite oxidizing bacteria are the key steps of nitrification Previous studies have focused on their effects in acidic neutral and weakly alkaline soils However there are few studies on nitrification in extremely saline soils with high productivity In order to understand the effect of combined addition of biochar and wood vinegar on nitrification and related nitrifiers in extremely alkaline soils under rice cultivation we collected extremely alkaline soils to carry out a pot experiment under four different treatments: fertilizer only biochar wood vinegar and biochar wood vinegar The main results were as follows the addition of biochar and/or wood vinegar reduced the soil pH and increased the soil nutrient contents The addition of biochar and/or wood vinegar both significantly increased the abundances of AOB and Nitrobacter while there was no significant effect on the abundances of AOA and Nitrospira Compared to CK biochar and/or wood vinegar significantly decreased the relative abundance of Clade A of Cluster 11b of partial AOA and Nitrosospira Group 3a1 of AOB yet increased Nitrosomonas Group 7 of AOB A structural equation modeling showed that the abundance of AOA and AOB had direct and indirect effects on ammonium nitrogen nitrate nitrogen and potential nitrification rate Redundancy analysis showed that nitrifying community structures were significantly affected by pH and nutrient contents In general the abundance diversity and community composition of AOB contributed more to PNR than AOA in soils with extreme alkalinity It is important to understand their effect on soil nitrification for the application of biochar wood vinegar in practical production