Mobilization of soil phosphorus during passage through the gut of larvae of Pachnoda ephippiata (Coleoptera: Scarabaeidae)

Soil macrofauna play important roles in the mobilization of soil nutrients. The influence of gut passage on soil phosphorus availability was investigated using the larvae of the scarabaeid beetle Pachnoda ephippiata. Gut passage significantly increased the levels of available P in the feces over that of the soil consumed. ³¹P-NMR recorded the changes in the nature of organic P in alkaline extracts from gut content. Alkaline phosphatase activity was high in the alkaline midgut, but low in the hindgut and soil. Ferric iron (Fe³⁺) in the soil was reduced to ferrous iron (Fe²⁺) in the gut. The amount of Ca²⁺ was lower in the gut than in the soil. Iron reduction and the decrease of Ca²⁺ concentration in the gut would reduce P sorption. We think that the following effects are responsible for increased availability of P during the gut passage: alkaline extraction of soil organic matter; hydrolysis of organic phosphate esters with alkaline phosphatase; digestion by the resident microorganisms; and changes in the concentration of metal ions during gut passage. This study suggests that the feeding activities of humivorous larvae would affect the amount of soil P available to plant growth.