In the present study, the potassium-solubilizing characteristics of Bacillus aryabhattai SK1-7 and its growth-promoting effect on plants were evaluated to determine the biotechnological potential of this bacterium in alleviating soil potassium deficiency. The potassium-solubilizing activity of SK1-7 was determined by fermentation. Additionally, the fermentation broth was determined by flame spectrophotometry. The aluminum and silicon ion contents in SK1-7 fermentation broth were determined by inductively coupled plasma-atomic emission spectroscopy (ICP-AES) after digestion with nitric acid hydrogen peroxide hydrofluoric acid. Scanning electron microscopy (SEM)-based observations were performed to assess the morphological changes in potassium feldspar surfaces digested by potassium-solubilizing bacteria. In addition, the effects of SK1-7 on plant growth and soil physical and chemical properties were analyzed. After incubation for 7 days in a potassium-solubilizing medium, the concentration of potassium dissolved reached 10.8 μg/mL and the percentage of potassium released was 32.6%. The pH rapidly decreased from 7.2 to 4.321 within the first day and then further decreased to 3.90 after 7 days. After 7 days, the concentrations of aluminum and silicon in the fermentation broth were 1.01 and 24.19 μg/mL, respectively. The growth promotion assay results showed that SK1-7 has good growth-promoting effects on poplar and can effectively improve the available potassium content in poplar rhizosphere soil. The SK1-7 strain can effectively dissolve insoluble potassium to release soluble potassium ions and clearly promotes the growth of poplar after being applied to soil. Thus, the SK1-7 strain is a potassium-solubilizing microorganism with good application prospects.
The pine wood nematode (PWN) Bursaphelenchus xylophilus is recognized as a major invasive species in many countries and causes widespread mortality in pine trees. Pine wood nematode disease (PWD) has spread northward from southern China to several areas of Liaoning Province, which has temperatures outside of the optimal range for this disease. To determine whether obvious variations in the population adaptability of PWN are involved in its rapid spread from southern to northern China, this study compared the differences in morphology of eight southern strains and eight northern strains and the pathogenicity of the 16 strains to Pinus thunbergii, the pine species that is the most susceptible to PWD in China, and to P. tabuliformis, the main PWN host in northern Liaoning Province. The southern-strain females were smaller than the northern-strain females, except for strain GD32. The size differences between the males of the different strains were not significant. The difference in pathogenicity between the northern and southern strains to P. tabuliformis was more significant than the difference in their pathogenicity to P. thunbergii. The pathogenicity differentiation among northern strains was lower than that among southern strains, and the northern strains showed stronger pathogenicity to P. tabuliformis. The P. tabuliformis inoculation experiment showed that the pathogenicity of GD32, JS27, FJ14, LN13, and LN06 was significantly higher than that of FJ13. The results suggest that some PWN populations in the southern region, which are better adapted to P. tabuliformis, were likely directly transmitted to the northern region, resulting in the spread of PWD in the northern region. The spread of PWN from the south did not necessarily require a process of adaptation to the host or to the northern climate.
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