Biochar Wood Vinegar Altered the Composition of the Inorganic Phosphorus Bacteria Community in Saline-Alkali Soils and Promoted the Bioavailability of Phosphorus

As an important part of the ecosystem, saline-alkali soils are in urgent need of efficient and environmentally friendly soil conditioners. Biochar (BC) and wood vinegar (WV) are regarded as organic soil improvement and plant growth regulators to improve soil physical and chemical properties and promote crop growth, however, the mechanism of how inorganic phosphorus (Pi) bacteria increase phosphorus (P) when biochar and wood vinegar are applied in saline-alkali soils is not clear. The present study was designed to investigate the effects of BC and WV on the physical and chemical properties of saline-alkali soils and the diversity of Pi bacteria and to discuss the mechanism of BC and WV on available phosphorus (AP). Soil samples were collected from pot experiment with different rates of BC and WV (control without BC and WV, 0.6 ton· ha−1 BC, 0.6 ton· ha−1 WV, 1.2 ton· ha−1 WV, 1.8 ton· ha−1 WV, 0.6 ton· ha−1 BC and 0.6 ton· ha−1 WV, 0.6 ton· ha−1 BC and 1.2 ton· ha−1 WV, 0.6 ton· ha−1 BC and 1.8 ton· ha−1 WV). Application of BC and WV exhibited an effect on the decrease of pH and salt contents and the increase of soil porosity (SP), soil organic matter (SOM), and hundred-grain weight of rice. Single and mixed application of biochar and wood vinegar had no significant effect on total phosphorus (TP) and total nitrogen (TN), but increased available phosphorus(AP), available nitrogen(AN), and available potassium(AK), which were the best in the BC_WV3 group, increasing by 49.24%, 18.41%, and 45.03%, respectively. The addition of BC and WV enhanced microbial biomass phosphorus (MBP) concentrations and the 0.6 t· ha−1 BC and 1.2 t· ha−1 WV group with the largest increase by 41.29%. All groups improved phosphatase activities and the 0.6 t· ha−1 BC and 1.8 t· ha−1 WV group increased most in alkaline phosphatase (ALP), acid phosphatase (ACP), and neutral phosphatase (NEP) activities by 40.35%, 48%, and 149%, respectively. Moreover, BC and WV when applied to soils changed the composition and structure of Pi bacteria and promoted the diversity and abundance of Pi bacteria, more so at a higher rate of WV application.Redundancy analysis (RDA) and correlation analysis predicted that porosity, pH, and the richness of Alphaproteobacteria and Hydrogenophaga were the key factors determining AP. The main influencing factors for the diversity of phosphorus-solubilizing bacteria were SOM, saltness, and the richness of Bacteroidetes and Pseudomonas. In conclusion, the application of BC and WV was a useful strategy to improve saline-alkali soils, and the mixed-use of 0.6 t· ha−1 BC and 1.8 t· ha−1 WV had the best improvement effect.