Host species and nitrogen-fixing bacteria
Alnus hirsuta (Betulaceae; Alnus incana ssp.hirsuta Spach; Chen & Li 2004; Ren et al. 2010) is a deciduous, broad-leafed tree and an early successional species. It is widely distributed in temperate riparian forests in Japan, northeastern China, Korea, and Russia. Alnus trees have characteristics as a foundation species (Ellison et al., 2005; 2010; Kagiya et al., 2018), which is likely to have great impacts on forest ecosystems.
Frankia sp. (Frankiaceae) are actinobacteria with the ability to convert atmospheric nitrogen gas to ammonia. While Frankia that form nodules on roots of phylogenetically diverse host plants are gram-positive, rhizobia that form nodules on roots of legume plants are gram-negative.