Soil stocks of glomalin produced by arbuscular mycorrhizal fungi across a tropical rain forest landscape

1. Symbiotic arbuscular mycorrhizal (AM) fungi produce a recalcitrant AM-specific glycoprotein, glomalin, which could be a substantial contributor to soil carbon (C). In this study we made a first assessment of the standing stocks of glomalin in a tropical lowland rain forest (the La Selva Biological Station, Costa Rica) and tested whether glomalin concentrations varied over the strong fertility gradient in this forest. 2. Mean levels of glomalin in the top 10 cm of the La Selva soils were 3.94 +/- 0.16 mg cm(-3) (1.45 Mg C ha(-1)), accounting for approximately 3.2% of total soil C and 5% of soil nitrogen (N) in the 0-10 cm soil layer. 3. More fertile soils with higher concentrations of calcium, phosphorus and potassium had less glomalin, while the less fertile soils, those with high C: N ratios and high levels of iron and aluminium, had more glomalin. 4. We found higher levels of immunoreactivity, which is characteristic of young, recently produced glomalin, in the soils with higher concentrations of calcium, phosphorus and potassium. We hypothesize that AM fungal turnover, as indicated by a greater proportion of immunoreactive, recently produced glomalin, is enhanced in the more fertile soils within this tropical rain forest landscape.