Klebsiella oxytoca improves resistance of maize seedling to saline-alkali stress

Objectives The effects of Klebsiella oxytoca on the biological properties of saline-alkali soil were studied to provide a theoretical basis for developing suitable microbial fertilizer in saline-alkali areas.

Methods Zhengdan 958 variety of maize was used as the test material. Klebsiella oxytoca was induced to produce heritable resistant properties to 300 g/L antibiotic rifli. The resistant strains were inoculated in LB liquid medium and cultured at 180 r/min at 30℃ for 24 h. After centrifugation and washing, a bacterial suspension of 1×10⁸ cfu/m was prepared using distilled water. Thereafter, its nitrogen fixation, phosphorus dissolution, ammonium production, and IAA capacity were measured. The bacterial suspensions of 1×10⁶ cfu/mL, 1×10⁴ cfu/mL, and 1×10² cfu/mL were gradually diluted and prepared for pot experiment. The saline-alkali soil (pH 9.4) was collected from Zhaodong City, Heilongjiang Province. Klebsiella oxytoca was added to the soil at 0, 1×10², 1×10⁴, 1×10⁶ and 1×10⁸ cfu/mL, followed by the planting of germinated maize. The photosynthetic characteristics of maize seedlings were measured after the second leaf unfolds. The seedlings were harvested after 12 days of growth. Plant height, root length, aboveground dry weight, and underground dry weight of the maize seedlings were measured. The contents of C, N and P in maize leaves were determined. The activities of urease, alkaline phosphatase, sucrase and catalase in the rhizosphere of maize seedlings were determined using the root shaking method.

Results The total nitrogen fixation, soluble phosphorus content, IAA concentration and ammonia yield of Klebsiella oxytoca were 12.8 mg/L, 85.59 mg/L, 256.57 mg/L and 75.46 mg/L , respectively. Klebsiella oxytoca could colonize well in saline-alkali soil and reached a stable number of bacteria on the third day after application. In saline-alkali soil, the activities of urease, alkaline phosphatase, acid phosphatase and catalase in rhizosphere soil of maize seedlings increased with the increase of Klebsiella oxytoca application level. Compared with the control, the four enzyme activity (urease activity, alkaline phosphatase activity, sucrase activity, and catalase activity) was significantly increased(P<0.05)in all the treatments, with 1×10⁶ cfu/mL recording the highest value. The urease activity, alkaline phosphatase activity, sucrase activity, and catalase activity increased by 62.81%, 17.74%, 115.5%, and 35.6% compared with CK. Klebsiella oxytoca applied at 1×10⁶ cfu/mL significantly reduced the salt ions in leaves, increased photosynthetic capacity, increased plant height by 12.44%, root length by 22.59%, aboveground dry weight by 26.67%, and underground dry weight by 37.78% compared with CK.

Conclusions Klebsiella oxytoca is capable of fixing N, dissolving phosphorus and secreting auxin. Klebsiella oxytoca can significantly increase enzyme activity in the rhizosphere, decrease Na⁺ content in maize seedlings, increase the contents of K⁺ and Ca²⁺ and the ratio of K⁺/Na⁺ and Ca²⁺/Na⁺. Further, it significantly improves the photosynthetic efficiency and salt-alkali tolerance of maize seedlings and promotes the growth of maize. However, the effect of Klebsiella oxytoca depends on the application rate, and the specific field concentration requires further research.