Abstract: Soil phosphorus deficiency seriously affects rice production. In this study, we investigated the effects of biochar application and phosphorus-solubilizing bacteria (Bacillus megaterium 1.234) on rice seedling growth and phosphorus availability in rhizosphere under phosphorus stress in an indoor culture experiment. Six treatments were deployed, including Kimura B culture medium (CK₁), Ca₃(PO₄)₂ culture medium (CK₂), no phosphorus culture medium (CK₃), B. megaterium 1.234+Ca₃(PO₄)₂ culture medium (MP), B. megaterium 1.234+biochar+Ca₃(PO₄)₂ culture medium (MBP), biochar+Ca₃(PO₄)₂ culture medium (BP). The results showed that plant height of 20-day-old seedlings under MBP treatment was increased by 21%, 35%, and 23% compared with CK₁, CK₂, and CK₃, respectively. The weight of dry matter was increased by 11%, 17% and 21%, respectively. Total phosphorus content of seedlings was increased by 179%, 277%, and 199%, respectively. Moreover, MBP treatment significantly increased total root length, total root surface area, total root volume, and root tips. Compared with CK₂ treatment, MBP treatment increased soil available phosphorus content by 309% and the activities of acid phosphatase and alkaline phosphatase by 444% and 284%, respectively. The available phosphorus content in the culture medium was the most important environmental factor affecting the growth of rice seedling roots, alkaline phosphatase activity, and available phosphorus content in the culture medium were the key environmental factors affecting growth and total phosphorus content of rice seedling. In conclusion, the combined application of biochar and phosphorus solubilizing bacteria had significant promoting effects on the growth of rice seedlings under phosphorus deficiency.

Key words: root morphology, acid phosphatase, alkaline phosphatase, rice phosphorus uptake, microbial fertilizer.