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This study evaluated the potential of biochar derived from the brown macroalga, Eisenia bicyclis, which is widely distributed along the Japanese coast, as a functional soil amendment and microbial attachment substrate. Marine macroalgae are characterized by rapid growth and high photosynthetic capacity, contributing to effective CO₂ fixation; however, stranded algae often accumulate as an environmental burden. Conversion of macroalgal biomass into biochar represents a promising strategy for the sustainable utilization of marine algal resources. Accordingly, biochars derived from E. bicyclis were produced at three pyrolysis temperatures (350, 450, and 550 °C), and their properties were evaluated in comparison with lignocellulosic biochars obtained from wood and rice husk, using elemental analysis and Fourier-transform infrared (FTIR)-based surface functional group characterization. Subsequently, to assess functional performance in soil, the biochars were added to agricultural field-collected soil and incubated for 28 days, after which microbial attachment was quantified using ATP-based biomass measurements and visualized by SEM. The results showed that algae-derived biochars contained higher concentrations of nitrogen and mineral elements than lignocellulosic biochars. Among the tested conditions, biochar produced at 450 ℃ exhibited recalcitrance comparable to that of wood- and rice husk–derived biochars. When biochars with comparable recalcitrance were applied, microbial attachment levels were similar regardless of feedstock type, and microbial aggregates were consistently observed on the biochar surfaces. These findings demonstrate that E. bicyclis–derived biochar is a nutrient-rich and persistent material that supports soil microbial colonization, highlighting the value of marine macroalgal biomass for agricultural and environmental applications.
Research papers (academic journals)
