Ecological Context of Bioavailable Phosphorus in Sub-Boreal Forests of Northern Japan: Interactive Effects of Fire and Earthworm Disturbances.

Fire is an important driver of ecosystem processes yet very little is known about its effect on soil phosphorus (P), which is often a limiting or co-limiting nutrient in northern Japanese soils. Soil microbes and fauna, such as earthworms, provide an essential function in forest ecosystems by transforming nutrients into plant available forms via cast production. Simultaneously, plants chemically alter the rhizosphere to enhance bioavailability of soil P. The purpose of this study was to assess the interactive effects of fire and soil earthworm activity in contrasting soil types of northern Japan using the biologically-based P (BBP) extraction method, which mimics a variety of plant P acquisition strategies. In a fully factorial laboratory experiment, we combined soils developed on serpentine and sedimentary parent materials with a common earthworm species, Aporrectodea rosea, and 500 kg ha-1 pulverized charcoal. Microcosms were maintained at 60% water holding capacity with free air exchange at a constant temperature of +15°C for 4 weeks. Each treatment was replicated five times (n = 5) for a total of 40 individual microcosms. Soils were extracted in parallel before and after the incubation period by the BBP method with 10 mM CaCl2 (measures soluble P), 10 mM citric acid (chelate extractable P), phytase and phosphatase solution (enzyme extractable organic P), and 1M HCl (mineral occluded P). We provide a context for biological activity and forest disturbance that is likely to alter soil P bioavailability in northern Japan. The forests of northern Japan represent a transition from cold boreal forests to warmer, biologically diverse temperate forests and may provide an example for future forests in a climactically altered zone.