Combining ectomycorrhizal fungi and plant growth-promoting rhizobacteria to enhance salt tolerance of Metasequoia glyptostroboides

Plant growth and productivity are negatively affected by soil salinity. This study investigated the effects of the rhizosphere-promoting bacterium, Bacillus paramycoides JYZ-SD5, and the ectomycorrhizal fungus, Schizophyllum commune Be, on the growth of Metasequoia glyptostroboides under salt stress. Changes in biomass, root growth, root ion distribution and in vivo enzyme activities were determined under different treatments (Be, JYZ-SD5, and Be + JYZ-SD5). The results show that all inoculations increased chlorophyll content, shoot length and root diameter with or without salt stress, and the effect of Be + JYZ-SD5 was the strongest. JYZ-SD5 and Be + JYZ-SD5 treatments significantly increased root length, surface area, bifurcation number, tip number, main root length and diameter under salt stress. Normal chloroplast structures developed under both single and double inoculations. Relative to the control, root activities of M. glyptostroboides in the Be, JYZSD5, and Be + JYZ-SD5 treatments increased by 31.3%, 17.2%, and 33.7%. All treatments increased the activities of superoxide dismutase (SOD), peroxidase (POD), Na+-K+- ATPase and Ca2+-Mg2+-ATPase. The strongest effect was by Be + JYZ-SD5. Analysis of root ion distribution showed that, under salt stress, Na+ and K+ decreased and were concentrated in the epidermis or cortex. Na/K ratios also decreased. The Be + JYZ-SD5 treatment increased betaine by 130.3% and 97.9% under 50 mM and 100 mM salt stress, respectively. Together, these changes result in the activation of physiological and biochemical processes involved in the mitigation of salinity-induced stress in M. glyptostroboides.