Characteristics of nickel accumulation in native plants growing in ultramafic rock areas in Hokkaido

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Abstract
Nickel accumulation in the native plants growing in ultramafic rock areas in Hokkaido, Japan was studied. The mean soil pH ranged from 6.1 to 8.0. The content of exchangeable Ni in the soil was only 3 to 13 mg kg−1. The lowest content of total Ni was 1.3 g kg−1, and the highest value was 2.6 g kg−1. Thlaspi japonicum was found to accumulate as much as 1,045 mg Ni (kg dry wt)−1, although this species is not an ultramafic plant. Five other species, Allium schoenoprasum var. sibutuense, Viola yubariana (endemic species on Mt. Yupari), Lagotis takedana (endemic species on Mt. Yupari), Viola sacchalinensis var. alpina, and Draba japonica were identified as strong Ni accumulators based on measurements using dried herbarium specimens. The Ni content in ultramafic plants exceeded 50 mg (kg dry wt)−1 in about half of the native plants growing in ultramafic rock areas. The Ni content of dried plants of Allium schoenoprasum var. sibutuense was 234 mg (kg dry wt)−1, while that of Allium maximowiczii was only 19 mg (kg dry wt)−1. Although Deschampsia caespitosa var. levis, Japonolirion osense var. saitoi, Betula apo iens is , and Primula hidakana are ultramafic plants, the Ni content in these plants was less than 10 mg (kg dry wt)−1. In all the examined ultramafic plant species, the Ni content in plants plotted against the exchangeable Ni content in soil was represented by a regression curve and not a straight line. The Ni content in plants increased markedly with increasing exchangeable Ni content in soil in a low content range, but slightly in a high content range. In common plants, a similar correlation was observed only in one species, a linear correlation in three species and no correlation in two species.