To aid in the restoration of coastal barren ground areas, it is important to clarify the effects of chelated iron on the growth of seaweed. In particular, for the further development of practical methods to promote seaweed growth, Fe-binding organic ligands, such as humic substances (HSs) composed of humus materials, rather than Fe-binding inorganic ligands, such as ethylenediaminetetraacetic acid (EDTA), should be investigated. In this study, the effects of an Fe-fertilizer, made from HSs and steelmaking slag, on the growth of Sargassum horneri at the germling and immature stages were examined. The addition of the Fe-fertilizer eluate containing Fe-organic ligand complexes clearly promoted the growth of Sargassum horneri at the germling and immature stages. It was also clear that the effect of Fe concentration in the Fe-fertilizer eluate on the growth rate was almost the same as that of Fe-EDTA. Moreover, the addition of the Fe-fertilizer eluate had a great effect on the brown color of Sargassum horneri thalli and promoted the increased content of photosynthetic pigments, such as Chl. a. Based on these experimental results, the application of the Fe-fertilizer containing Fe-organic ligand complexes is expected to become an effective method for the restoration of the barren ground phenomenon in Fe-deficient coastal areas.
Sargassaceae species are important macroalgae for maintaining marine environments. Furthermore, biofuel based on Sargassaceae species has become studied recently. However, Sargassaceae species have declined rapidly in coastal areas around Japan, which are called "isoyake", a term meaning barren areas. The development of effective measures to restore these "isoyake" and the construction of Sargassaceae beds are strongly needed. A lack of iron in coastal areas limits the growth of macroalgae, and may cause "isoyake". However, the effects of the iron concentration on the growth of macroalgae, such as species of Sargassaceae, are poorly studied. In this research, the effects of chelated iron on the growth of Sargassaceae species during the germling and immature stages were examined. The addition of Fe-EDTA promoted the growth of four Sargassaceae species during the germling stages. During the germling stage of Sargassum ringgoldianum, the maximum specific growth rate and the saturation constant were estimated to be 0.17 day -1 and 4.3 μg/L, respectively. Additionally, the periodic addition of Fe-EDTA promoted the stable growth of Sargassum horneri during the immature stage.
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