Effect of inoculating rhizobia on growth and physiological characteristics of Ormosia hosiei seedlings

The Ormosia hosiei is a unique and precious native wood species in China, which is listed as a key protected wild plant. This study aims to investigate the effects of inoculating different rhizobia on the growth and physiological indicators of O. hosiei seedlings, to reveal the growth-promoting effects of different rhizobia on O. hosiei seedlings and screen out efficient rhizobial strains for cultivating strong seedlings of O. hosiei.

O. hosiei seedlings were inoculated using eight rhizobial strains, and the effects of rhizobial inoculation on growth traits, nodulation status, leaf nitrate reductase activity, leaf nitrate nitrogen content, chlorophyll content, photosynthetic rate, and other indicators were analyzed. The seedling quality was evaluated by using a principal component comprehensive evaluation.

The growth and physiological performance of O. hosiei seedlings inoculated with rhizobia were superior to those of seedlings without inoculation. Compared with the seedlings without inoculation, the increases in height, ground diameter, and total biomass of the seedlings inoculated with rhizobia were 25.75%-96.49%, 17.31%-51.16%, and 42.11%-102.63%, respectively. The increases in total root length, total root surface area, average root diameter, and total root volume were 14.88%-201.33%, 17.56%-169.76%, 2.38%-23.81%, and 40.98%-190.16%, respectively. The increases in chlorophyll content, net photosynthetic rate, transpiration rate, nitrate reductase activity, and nitrate nitrogen content were 2.14%-66.31%, 27.36%-209.43%, 71.88%-337.50%, 31.30%-191.60%, and 2.33%-48.84%, respectively. The order of comprehensive quality scores of O. hosiei seedlings inoculated with different rhizobial strains was: No.5 > No.6 > No.4 > No.8 > No.2 > No.7 > No.1 > No.3.

Inoculation with rhizobia could significantly improve the physiological status of O. hosiei seedlings and promote their growth and biomass accumulation. Among them, strains No. 4, No. 5 and No. 6 have better growth-promoting effects and could be used as excellent strains for cultivating strong seedlings of O. hosiei.