Interactive effects of charcoal and earthworm activity increase bioavailable phosphorus in sub-boreal forest soils

Abstract

The purpose of this study was to assess the effects of charcoal and earthworm presence in contrasting soil types of northern Japan using the biologically based phosphorus (BBP) extraction method, which employs a variety of plant P acquisition strategies. Using soils developed in serpentine and sedimentary parent materials, we tested the interactive effects of Eisenia japonica (Michaelsen) earthworms and 500 kg ha−1 of dwarf bamboo charcoal (Sasa kurilensis (Rupr.) Makino et Shibata) in a microcosm incubation that lasted four weeks. Soils were extracted in parallel after the incubation with the BBP method using 0.01 M CaCl2 (soluble P), 0.01 M citric acid (chelate-extractable P), 0.02 phosphatase enzyme units ml−1 (enzyme-extractable organic P), and 1.0 M HCl (mineral occluded P). Dwarf bamboo charcoal alone contained up to 444 mg total BBP kg−1 prior to application to soil microcosms. Treatment effects in soil microcosms were highest in sedimentary soil types and where charcoal was combined with earthworms (15.97 mg P kg−1 ± SE 1.23 total inorganic BBP). Recalcitrant inorganic P (HCl extracted) in combination treatments yielded the highest single inorganic BBP measure (12.41 mg kg−1 ± SE 1.11). Our findings suggest that charcoal, as a legacy of wildfire, and native earthworm activity may help stimulate cycling of recalcitrant inorganic BBP pools.