Study sites
Our study sites are located in and around Uryu Experimental Forest, Japan (44°030–290N, 142°010–200E), a natural conifer-broadleaf mixed forest. Sampling of rhizosphere and riparian soils and root nodules from alders was conducted in 12 sites along four river areas (see also Kagiya et al. 2018). Only Alnus hirsuta exist in these sites actinorhizal plants.