Comparison of salinity tolerance using the seawater immersion test for 20 tree species commonly found in coastal forests of western Japan

Abstract

Salinity tolerance after seawater immersion treatment was surveyed for 20 tree species commonly found in coastal areas of western Japan to classify them as alternatives to Pinus thunbergii predominantly composing coastal disaster reduction forests. First, the Fv/Fm values and the number of fallen leaves were monitored for 10 saplings planted in 10.5 cm pots with horticultural soil, including three control saplings, of each species for 50 days after the seawater treatment. Then, their recovery or declining process was observed for seven months. The behavior of saplings after the seawater treatment was diverse for each species, ranging from no change for P. thunbergii to immediate death within six days for Aphananthe aspera. Cluster analysis detected three groups: 1) salinity-tolerant species comprising P. thunbergii and three shrubs Eurya emarginata, Rhaphiolepis indica var. umbellata, and Euonymus japonicus; 2) six salinity-sensitive species such as Morella rubra and Castanopsis sieboldii; and 3) 10 intermediate species including arboreal broad-leaved evergreen trees such as Cinnamomum camphora, Litsea coreana, and Elaeocarpus sylvestris var. ellipticus. Electrical conductivity of leaching water from the bottom of sapling pots was still significantly higher than the pretreatment value on the 50th day after the treatment, therefore the saplings appeared to be exposed to salinity stress throughout the experiment period. It could be important to select sites with a relatively lower risk of seawater immersion due to storm surges, such as inland and elevated sites, when installing arboreal broad-leaved trees in coastal disaster reduction forests as an alternative to P. thunbergii.