Biochar and wood vinegar amendments influence the potential nitrification rate and nitrifier communities in high pH sodic saline soils

Nitrifiers are the key player in the nitrogen cycle of agroecosystems, yet less research has focused on their performance and response in saline ecosystems. In this study, we carried out potting experiments with biochar and wood vinegar as saline soil amendments under rice cultivation conditions with four different treatments: without biochar or wood vinegar (CK), biochar (BC), wood vinegar (WV), and biochar + wood vinegar (BC + WV). The results showed that the addition of biochar and/or wood vinegar decreased the soil pH and electrical conductivity (EC), which led to an increase in the gene abundance of ammonia-oxidizing bacteria (AOB), thereby benefiting the advancement of the potential nitrification rate (PNR). WV and BC + WV significantly increased the gene abundance of Nitrospira. In addition, the addition of biochar and wood vinegar altered the community composition of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), while the NH₄⁺-N content was the key factor affecting the nitrifier communities. Compared to the CK group, biochar and/or wood vinegar significantly increased the relative abundance of Nitrosospira cluster 3 b in AOB and unknown affiliation in nitrite-oxidizing bacteria (NOB). Overall, the abundance and community composition of AOB contributed more to the PNR than those of AOA, while NOB played a pivotal role in the potential nitrite oxidation (PNO) rate in sodic saline soils. In conclusion, the addition of biochar with wood vinegar had positive effect on improving sodic saline soils by improving the physicochemical properties of the soils, increasing the abundance of nitrifier and changing the community structure of nitrifier. Exploration of the key drivers of soil nitrifier processes is potentially useful for understanding the biological potential of nutrient cycling, providing novel insight into the effects of human intervention and soil management.