Differences in growth characteristics and dynamics of elements in seedlings of two birch species grown in serpentine soil in northern Japan

摘要

Seedlings of two birch species were grown in serpentine soil, with Betula ermanii showing high tolerance. Betula ermanii and Betula platyphylla var. japonica, two typical light-demanding-deciduous trees in northern Japan, usually invade disturbed areas. B. ermanii can invade serpentine soil and grow in it, whereas B. platyphylla var. japonica can hardly regenerate in it. Serpentine soil is distributed throughout Japan and is characterized by excessive Mg and heavy metals (Ni, Cr, and Co) which can lead to suppressed plant growth. We examined the tolerance of the two Betula species by planting seedlings in serpentine and non-serpentine (brown forest) soils. The dry mass of each organ was suppressed in both birches planted in serpentine soil, and the photosynthetic rate was reduced by accumulation of Ni. Also, uptakes of K and Ca were inhibited by accumulation of Mg, Ni, Cr and Co. B. ermanii planted in serpentine soil showed high value of net assimilation rate in the second year and maintained the photosynthetic rate from June to September. The effects of Mg, Ni, Cr and Co accumulation were small on the relative growth rate of B. ermanii. In contrast, B. platyphylla var. japonica planted in serpentine soil showed decreased photosynthetic rate in September and smaller net assimilation rate than B. ermanii at the same time. In addition, B. platyphylla var. japonica showed decreased relative growth rate, induced by accumulation of Mg in leaves and Co in roots. We conclude that B. ermanii has the high advantage of regenerating in serpentine soil.