Beneficial effect of hydrogen uptake ability on survival of bradyrhizobium japonicum in soil aggregate

Abstract

The relationship between the hydrogen uptake ability of rhizobia and their survival in soil was examined in two kinds of experiments. Indigenous rhizobia in soil were separated by a centrifugation-sonication technique into two populations differing in their location in the soil; the inner and outer areas of the soil aggregate. Each fraction was inoculated to soybean, and the nodules formed on the plants were assayed for acetylene reduction and hydrogen evolution by gas chromatography. Relative efficiency (RE) in nitrogen fixation of each nodule was assumed to be an indication of the hydrogen uptake ability of the rhizobia which formed the nodule. When the soils were incubated at 30°C for 14 days at 60% WHC moisture content, the inner fraction showed a higher ratio in the frequency of rhizobia with a RE value above 0.8 than the outer fraction, after compared to before soil incubation, respectively. Eight strains of antibiotic-resistant Bradyrhizobium japonicum, which showed different RE values, were separately incubated in the non-sterilized soil at 30°C, and viable counts in the two soil fractions were estimated. A strain exhibiting a higher RE value showed a higher ratio of viable count at 14 days of incubation compared to that at 0 day in the inner fraction. There was no correlation between the RE and survival ability of the strains in the outer fraction. These results suggest that the hydrogen uptake ability of rhizobia contributes to their survival in the inner area of the soil aggregate.

Key Words:

• Bradyrhizobium japonicum
• hydrogen uptake
• nodule
• soil aggregate