Abstract: This work aims to explore the performance of promoting growth and stress resistance of JYZ-SD5,a tree rhizobacterium,and to reveal the value of this bacterium in the field. Specific culture medium was used to detect its ability of nitrogen fixation and decomposition of phosphorus and potassium,also to measure its capacity of producing IAA. Then plate confrontation was employed to check the antagonistic activity to pathogenic fungi,and growth was observed to determine its tolerance to heavy metals. Further,the tree rhizobacterium JYZ-SD5 was applied to the seedlings of Metasequoia glyptostroboides Hu et Cheng in plots to test its effects on the growth of the seedlings. Morphology observation,physiological and biochemical tests,and 16S rRNA gene sequence analysis were combined to identify the strain JYZ-SD5. Results showed that JYZ-SD5 had the ability of fixing nitrogen and decomposing phosphorus and potassium. The production of IAA without adding tryptophan reached 6.818 6 μg/mL. JYZ-SD5 presented the antagonistic activity to Alternaria sp and Pestalotiopsis vesicolor,and protease and cellulose were also detected. This strain also demonstrated strong tolerance to heavy metals Mn⁷⁺ and Cr⁶⁺,to the highest content of 400 mg/L. The greenhouse plot experiment revealed that JYZ-SD5 resulted in the increase of relative content of chlorophyll in the seedlings of M. glyptostroboides Hu et Cheng,and it promoted the growth and ground diameter of M.glyptostroboides Hu et Cheng. Finally,the rhizobacterium was identified as Bacillus paramycoides by morphological,physiological,biochemical,and molecular approaches. In sum,the rhizobacterium JYZ-SD5 shows favorable performance on promoting growth and stress resistance,and thus it has the potential to be a novel biological fertilizer and meets the requirement of applying it in field.

Key words: molecular identification, growth-promoting property, adverse-resistant characteristics, species identification