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This study investigates the potential of moss species for extensive green roofs to achieve very shallow substrate, low maintenance and low cost green roofs. The performance of four moss species (Didymodon constrictus, Eurhynchium hians , Polytrichum commune and Racomitrium japonicum) were assessed using three kinds of substrate: (a) a mixture of clay soil and compost, b) baked black soil and c) river sand for two years in Chiba, within the Tokyo region of Japan. The individual species were grown in monoculture in 4 cm depth of substrate in trays on a rooftop without supplemental irrigation using an onsite propagation method. Although all four species became dormant in conditions of high temperature and little rain, it was possible for all to establish and survive. R. japonicum showed the greatest coverage among the four species, reaching 70%–80% cover in the first four months. P. commune performed almost as well but took over a year to reach consistently high coverage. E. hians coverage fluctuated greatly in response to drought events. D. constrictus had low coverage overall but grew slightly more in the clay/compost soil; P. commune did poorly in sand substrate; R. japonicum and E. hians showed no consistent differences in how they were affected by substrate type. After two years only R. japonicum and P. commune had high enough coverage to consider further investigation. R. japonicum is already used in green roofing and wall applications. This study suggests that while some mosses show high performance across substrate types, others can be used on green roofs to achieve high cover, but only after determining a suitable substrate type. These results can inform moss species selection for green roofs in Japan, however, this methodology can be applied in other regions to establish moss green roofs. An onsite propagation method can be used to establish moss green roofs but further research is needed to identify means of increasing onsite growth rates for more species. [ABSTRACT FROM AUTHOR]

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Several years after the Fukushima Daiichi Nuclear Power Plant accident, the surface mineral soil layer is believed to be the main reservoir of radiocesium (137Cs) in forest ecosystems in Japan. Dissolved 137Cs combines with clay minerals in the soil, and hence, it is not expected to easily infiltrate over time. However, previous studies have indicated that 137Cs derived from the older global fallout migrated deeper than that of the Chernobyl accident, and this cannot be explained by only the dissolved 137Cs vertical migration in the soil. Considering the carbon and nutrient dynamics in the forest floor, the 137Cs transfer process in soil via roots may alter its vertical distribution on a decadal scale. Therefore, in this study, we investigated the 137Cs activity concentrations in both roots and soil matrix, by considering four (0–20 cm) or six (0–30 cm) mineral soil layers taken at every 5 cm at seven study sites dominated by one of the six plant species (three coniferous forests, one deciduous forest, two deciduous forests covered by Sasa, and one bamboo forest) in eastern Japan in 2013. Comparing the results of 137Cs activity concentrations between roots and soil matrix taken at the same soil layer, roots at the surface (0–5 cm) layer often showed lower values than the soil matrix. However, roots deeper than 5 cm had higher activity concentrations than the soil matrix, conversely. The 137Cs inventories ratio of roots to soil matrix are about 1% at the 0–5 and 5–10 cm soil layer, and about 2% at the soil layers deeper than 10 cm. These results suggest that decomposition of root litter little affect the short-term vertical migration of 137Cs in the forest soil. However, it indicates that continuous production and mortality of roots with relatively high 137Cs activity concentrations have an important role for changing the vertical distribution of 137Cs on time scale of decades, particularly at deeper soil layers. • We evaluated whether root turnover contribute for changing the vertical distribution of 137Cs in soil matrix. • 137Cs inventory ratio of roots to soil matrix are 1% at shallow soil layer (0–10 cm) and 2% at the layer deeper than 10 cm. • Continuous root turnover can change the vertical distribution of 137Cs in soil on time scale of decades. [ABSTRACT FROM AUTHOR]