Distribution of Frankia and ectomycorrhizal fungi in a denuded volcanic soil exposed by a landslide during heavy rainfall caused by typhoon No. 26 (Wipha) in 2013

In October 2013, shallow landslides occurred on the western slopes of Miharayama central cone on Izu-Oshima lsland, located about 120 km from Tokyo, Japan, caused by heavy rainfall during Typhoon Wipha (No. 26). In December 2013 and June 2014, we collected soils from different depths in a landslide-denuded area and an adjacent, intact forested area. We cultivated Alnus sieboldiana seedlings in these soils and examined the formation of root nodules of Frankia, a symbiotic nitrogen-fixing actinomycete, and ectomycorrhizal (EM) fungi on alder roots. Nodulation and EM formation were observed in samples from both areas, except in soil collected from 50 to 100 cm depths from the surface of the landslide-denuded soil. In June 2014, we found that Aln. sieboldiana seeds had dispersed from neighboring forests had germinated on the surface of the landslide-denuded soil. Root nodules and EM were found on the roots of 91.2 and 93.2% of 148 seedlings, respectively. According to a bioassay test and field observations, the dominant types of EM fungi that formed on the seedlings were Alpova and Tomentella. These results show that Frankia and some EM species may be important for vegetation recovery after landslides on this Island.