Acinetobacter calcoaceticus promotes the seedling growth of Lespedeza daurica under saline-alkaline stress

Abstract:

Lespedeza davurica is a grass for ecological restoration in the Loess Plateau. The saline-alkaline soil in the Loess Plateau greatly affects the growth and restricted the economic and ecological values of L. davurica. Inoculation of growth-promoting rhizobacteria is an important way to improve plant tolerance to saline-alkaline stress. [Objective] This study aims to reveal the effect and mechanism of Acinetobacter calcoaceticus in promoting the seedling growth of L. davurica under saline-alkaline stress, preliminarily disclose the potential growth-promoting mechanism of legumes, and provide a theoretical basis for the field application of this bacterium. [Methods] The potassium-containing medium was used to measure the potassium-solubilizing ability of two A. calcoaceticus strains isolated from L. davurica rhizosphere. The liquid fermentation method was employed to determine the production of siderophore and indole-3-acetic acid (IAA) by the two strains. Furthermore, we carried out petri dish and pot experiments to determine the growth-promoting effects of A. calcoaceticus on L. davurica seedlings under saline-alkaline stress. [Results] Strains DP25 and DP27 had the abilities to solubilize potassium and showed the siderophore production of 53.13% and 86.67% and the IAA production of 1.01 mg/L and 17.31 mg/L, respectively. Compared with the control, the inoculation of DP25 significantly improved the stem length and root length of L. davurica seedlings in petri dishes. The pot experiments showed that strains DP25 and DP27 had positive effects on the photosynthetic pigment synthesis and photosynthesis of the plants under saline-alkaline stress. Compared with the control, the inoculation with strains DP25 and DP27 increased the plant height, stem diameter, root surface area, total root length, and bifurcation number of L. davurica plants in pots. In addition, strain DP27 increased the aboveground biomass, underground biomass, root volume, total root tips, and root activity. [Conclusion] A. calcoaceticus demonstrates growth-promoting effect on the seedlings and adults of L. davurica. It secretes IAA to promote the growth of seedlings and improves the photosynthetic capacity and root morphogenesis to facilitate the growth of the adults under saline-alkaline stress. A. calcoaceticus can be used as a growth-promoting bacterium for planting L. daurica in the saline-alkaline area of Loess Plateau.