西表島海岸マングローブ林の土壌, 土壌水および葉の鉄, マンガン, イオウ, ホウ素およびタンニンについて

抄録

Mangrove trees grow under reductive soil conditions which is normally injurious to root growth. This study focused on discussing the mechanism of mangrove trees in adapting to soil conditions. In the forests of Rhizophora stylosa and Bruguiera gymnorrhiza which are developed along the coast and clearly distributed zonally, iron, manganese, sulfur, boron and tannins contained in the soil environment and leaves were analyzed. H₂S damage is alleviated by the fact that FeS₂ is formed by Fe²⁺ reacting with H₂S formed by the sulfate reduction. The quantity of FeS₂ was limited by the concentration of Fe²⁺ and SO₄-S in the soil water. However the concentration of Fe²⁺ was kept under except in landward sites. Thus we will assume that Fe²⁺ has eluted by the reductive effect of tannins. Otherwise the Fe²⁺ would be insufficient for forming FeS₂. The tannins have eluted with rather high concentrations to soil water from the roots at seaward sites, then Fe²⁺ and Mn²⁺ have eluted due to the tannins. At the seaward edge of R. stylosa the concentrations of Fe and Mn in leaves were high. Mn, especially, accumulated in high concentrations. The reason is that the reductive effect of tannins accumulated in high concentrations in leaves like Mn kept a balance with the oxidation effect of Mn. In addition, at the seaward edge of R. stylosa the concentrations of B in leaves were also high. The reason is that B is related to the formation of catechin that is one of the principal ingredients of the tannins. Thus we will assume that the tannins, Mn and B play important roles in adaptation under the reductive soil conditions. In addition, a change in the concentrations in leaves between R. stlosa and B. gymnorrhiza may limit the distribution.