The effects of earthworm (Lumbricus terrestris) activity on phosphorus availability in an Ontario podzol
Phosphorus availability in hardwood forest ecosystems growing on acidic, weathered soils is thought to rely on the efficient recycling of mineralized phosphorus through the humus layer. I hypothesized that high levels of earthworm activity in such systems would increase the concentrations of iron- and aluminium-associated phosphorus and reduce the proportion of soil phosphorus in labile inorganic forms by exposing phosphate mineralized from decomposing detritus to fixation by the mineral soil. Using a modified Hedley fractionation, I divided the phosphorus into six fractions of differing biological availability: Resin-P, Bicarb-Pi. Bicarb-Po, NaOH-Pi, NaOH-Po, and HCI-P. The introduction of ' L. terrestris' to podzolic soil in an incubation experiment revealed that earthworm activity, contrary to expectations, did not change the concentration of iron- and aluminium-associated phosphorus (NaOH-Pi) and increased the concentrations of the labile inorganic phosphorus fractions (Resin-P and Bicarb-Pi) as well as the proportion of extracted phosphorus found in these fractions. In addition, earthworm activity decreased the concentration of calcium-associated phosphorus (HCI-P). It is possible that earthworm activity reduced the phosphate adsorption capacity of the soil by increasing the formation of organic-mineral complexes. These findings suggest that earthworm activity could increase phosphorus availability in forest ecosystems.