Abstract:

The aim of this work was to expand microbial fertilizer strain resources and develop rhizobial agents suitable for Sesbania cannabina cultivation in saline-alkali soils. To this end， Rhizobium strains were isolated from the root nodules of S. cannabina growing in a trial planting area in saline-alkali land in Kashi， Xinjiang. The isolates were identified based on 16S rRNA gene sequences amplified by polymerase chain reaction， and by phylogenetic analyses. The effects of the isolated strains， alone or in mixed combinations， on the growth of S. cannabina and the properties of salt-alkali soil were determined. A total of 17 strains were isolated， belonging to the genera Ensifer， Enterobacter， and Brucella， with Ensifer being the dominant genus. The strains Ensifer sp. B-3-1， Ensifer sp. C-3-2， Enterobacter sp. A-5-1， and Brucella sp. C-4-1 exhibited the ability to solubilize both organic and inorganic phosphorus. Inoculation of Ensifer as single strains or mixed with other strains positively affected the growth of S. cannabina； the plant height， stem diameter， aboveground dry weight， chlorophyll content， and root dry weight were increased by 21.2%-56.2%， 22.3%-67.8%， 4.5%-43.5%， 26.8%-149.5%， and 18.2%-100.0%， respectively， and the number of root noduleswas also significantly increased （P<0.05）. The properties of salt-alkali soil were also improved by Ensifer strains， alone or in combinations； the pH value and total salt， total phosphorus， and total potassium contents were decreased by 2.4%-4.1%， 23.6%-39.1%， 23.3%-69.4% and 2.2%-21.2%， respectively， and the available nitrogen and available phosphorus contents were increased by 63.5%-98.4% and 0.1%-9.0%， respectively. After inoculation with Ensifer sp. B-3-1， the available potassium content in soil was lower than that of the control group， but inoculation with other Ensifer strains increased the available potassium content in soil by 8.4%-99.7%. Among the various tested combinations， the combination E （Ensifer sp. C-3-2， Ensifer sp. B-3-1， and Brucella sp. C-4-1） had the best effect. The strains re-isolated after inoculation were highly homologous to the inoculated strains B-3-1 and C-3-2， demonstrating their successful colonization of the host. The Rhizobium strains obtained in this study have potential applications in developing microbial fertilizers suitable for reclamation and ecological restoration of saline-alkali land.

Key words: rhizobia, Sesbania cannabina, saline-alkali land, Ensifer, microbial fertilizers