Distinct response patterns of soil bacteria to oxalate imply their role in buffering soil acidification: Evidence from red soils with long-term fertilisation regimes

Long-term chemical-only fertilisation (NPK) decreases soil pH, but this soil acidification is rarely reported with manure fertilisation (M). Soil acidification always leads to a negative effect on sustainable development. As oxalate oxidation is accompanied by soil alkalisation, it is still unknown how and to what extent bacterial oxalate oxidation in soils with different fertilisation regimes contributes to buffering of soil acidification. To assess the potential role of oxalotrophy in buffering soil acidification, two soils that underwent contrasted fertilisation regimes for over 30 years were used. The oxalotrophic communities were characterised based on a biomarker of oxalotrophic taxa (the frc gene), and their responsiveness to calcium oxalate (CaOx) addition was assessed. In addition, stable isotope probing was employed to explore the active bacteria responding to CaOx addition. Despite similar abundances of oxalotrophic bacteria between NPK and M soils before microcosm incubation, the M soil harboured more oxalotrophic bacteria belonging to Deltaproteobacteria, and the NPK soil was colonised by more oxalotrophic bacteria affiliated with Actinobacteria, Alphaproteobacteria, and Betaproteobacteria. In the incubation experiments, the M soil took half of the time that the NPK soil needed to deplete the added CaOx. The faster CaOx consumption rate could be explained by the higher functional redundancy and higher proportion of fast-response oxalotrophic taxa in M soil. The most dominant active oxalotrophic taxa were Oxalicibacterium and Burkholderia in the M and NPK soils, respectively. Furthermore, the better performance of oxalate oxidation was conjectured to contribute to a higher soil acidification buffering ability. This study obtained an important cue to the feasibility of active oxalotrophic taxa in buffering acidification in soils with different fertilisation regimes, which provides valuable evidence for exploring alternative ways for alleviating soil acidification.