Feeding and defecation of earthworms alters phosphorus forms and resource allocation to enzyme production in an arable Andisol

Context Phosphorus cycles in the soil through chemical and biological reactions, and earthworms have been suggested to alter P distribution in soil. Aims We investigated the effects of earthworms’ feeding and defecation on soil phosphorus forms and the biochemical and physicochemical properties of the soil. Methods Earthworms were cultured in an Andisol, which is characterized by a high P adsorption capacity, with the addition of dried rice straw compost at three different levels. We evaluated P forms and biochemical and physicochemical properties of soil without earthworms (Control), soil affected by earthworm activities (Burrow), and earthworm feces (Cast). Key results Earthworms increased available P (H2O-Pi and NaHCO3-Pi) in Cast compared with Control, but did not increase phosphatase activity. Earthworms may increase competition between P and organic matter secreted by the earthworms for adsorption sites in Andisol, contributing to the variation in P forms in the soil. Burrow soil had higher acid phosphomonoesterase (ACP) activity than both Cast and Control; however, no increase in H2O-Pi or NaHCO3-Pi, was detected in Burrow soil, likely reflecting lower soil pH induced by earthworm activity. The ratio of ACP activity to β-D-glucosidase (BG) activity was significantly negatively correlated with the available P concentration and could be explained by pH and H2O-Pi in a multiple regression analysis. The ratio of ACP activity to alkaline phosphomonoesterase (ALP) activity was significantly negatively correlated with pH. Conclusions and implications We suggest that the stoichiometry of extracellular enzymes in the soil is strictly regulated by pH and P availability, which was increased by earthworm activity and compost application even in Andisol with strong P adsorption capacity.