LAUSR

Abstract Biomass feedstock plays an important role in the formation of environmentally persistent free radicals (EPFRs) in biochars; however, no investigations have been done on the effects of different plant habitats on the formation of EPFRs, especially for algae. Therefore, Laminaria japonica, a large-scale artificially planted marine economic macroalgae, was collected from six different coastal mariculture zones in tropical, subtropical and north-temperate zones from south to north in China. Biochars were obtained at the pyrolysis temperatures of 200−700 °C, and EPFR signs were recorded by an X-band electron paramagnetic resonance (EPR) spectrometer. Temperatures of 300−500 °C were the appropriate for higher levels of spin concentrations, and lower (200 °C) and higher (600−700 °C) temperatures decreased the biochar-bound EPFRs. The types of EPFRs generally belonged to oxygen-centered radicals for biochars produced at 200 and 300 °C, a mixture of carbon- and oxygen-centered radicals for 400 °C biochar, and carbon-centered radicals for 500−700 °C biochars. Different habitats (growth environments) of L. japonica influenced the levels rather than the types of the resulting biochar-bound EPFRs. Pearson correlation analyses showed that biochar-bound EPFRs were significantly positively correlated with the contents of C (p   0.05). Overall, algae biomass-based biochars have the similar levels and types of EPFRs as lignocellulosic-biomass-based biochars, and the different growing habitats of L. japonica grown influence the formation and characteristics of EPFRs in the resulting biochars.