Dan Luo

Phosphorus deficiency severely limits crop yields and hinders sustainable agricultural development. Phosphate-solubilizing bacteria (PSB) are beneficial for crop growth because they enhance the uptake and utilization of phosphorus. This study explored the phosphorus-solubilizing, IAA-producing, nitrogen-fixing, potassium-solubilizing, and siderophore-producing abilities of three bacterial strains (Pantoea sp. J-1, Burkholderia cepacia Z-7, and Acinetobacter baumannii B-6) screened from the maize rhizosphere. A pot experiment was also conducted to explore the role of screened PSB in the growth of maize. Finally, the effects of the PSB on the physicochemical properties, enzyme activities, and microbial community structure of maize rhizosphere soil were analyzed. The results showed that strain Z-7 had the strongest abilities phosphorus solubilization, nitrogen fixation, potassium solubilization, and siderophore production, while strain J-1 exhibited the highest yield of IAA. The application of PSB promoted the growth of maize plants to different extents. Among the different treatments, the mixed bacterial treatment (J-1 + Z-7 + B-6) had the most potent growth promotion effect, and the consortium treatment significantly enhanced the activity of soil phosphatase. Soil pH, total phosphorus (TP), total potassium (TK), available phosphorus (AP), NH₄⁺-N, and NO₃⁻-N are key factors for the growth of maize plants. In addition, PSB significantly altered the microbial community structure in the maize rhizosphere soil, and the relative abundance of Proteobacteria increased by 16.07–69.10% compared to the control. These PSB have obvious growth-promoting abilities, with the potential to enhance crop productivity as excellent candidate strains for the development of biological fertilizers.

This study investigated the performance of thermophilic–mesophilic (T-M) and mesophilic–thermophilic (M-T) two-phase sludge anaerobic digestion at different inoculation proportions after a change in digestion temperature. After temperature change, the pH, total ammonia nitrogen (TAN), free ammonia nitrogen (FAN), solubility chemical oxygen demand (SCOD), and total alkalinity (TA) levels of two-phase digesters were between thermophilic control digesters and mesophilic control digesters. However, the volatile fatty acid (VFA) levels of two-phase digesters were higher than those of thermophilic or mesophilic control digesters. The bacteria communities of M-T two-phase digesters were more diverse than those of T-M. After a change in digestion temperature, the bacterial community was dominated by Coprothermobacter. After a change of digestion temperature, the relative abundance (RA) of Methanobacterium, Methanosaeta, and Methanospirillum of M-T two-phase digesters was higher than that of T-M two-phase digesters. In comparison, the RA of Methanosarcina of T-M two-phase digesters was higher than that of M-T two-phase digesters. The ultimate methane yields of thermophilic control digesters were greater than those of mesophilic control digesters. Nevertheless, the ultimate methane yield levels of M-T two-phase digesters were greater than those of T-M two-phase digesters. The ultimate methane yields of all two-phase digesters presented an earlier increase and later decrease trend with the increasing inoculation proportion. Optimal methane production condition was achieved when 15% of sludge (T-M15) was inoculated under mesophilic–thermophilic conditions, which promoted 123.6% (based on mesophilic control) or 27.4% (based on thermophilic control). An optimal inoculation proportion (about 15%) balanced the number and activity of methanogens of high-solid sludge anaerobic digestion.