Glomalin is a ubiquitous soil protein attributed to arbuscular mycorrhizas that has been operationally defined by a non-specific assay on a soil citrate extraction (Bradford-reactive protein fraction or BRF) and a specific ELISA test against a monoclonal antibody (Immunoreactive fraction or IRF). Soil glomalin can represent a significant proportion of soil carbon and nitrogen stocks. Globally, glomalin stocks also show greater correlation with ecosystem net primary productivity than many other soil variables, including other proxies of mycorrhizal productivity. At a regional and local scale, glomalin has been shown to vary in response to factors affecting mycorrhizal dynamics across landscapes.

Results/Conclusions

In a series of studies in wet tropical regions we show that patterns of glomalin accumulation can be associated with variation in soils and vegetation, similarly for both glomalin fractions. At a more local scale, we also discovered a novel reservoir of glomalin in tropical soils that is associated with canopy tree species with abundant epiphytic plant communities. Glomalin levels in epiphytic soils were one to two orders of magnitude greater than in the forest floor, and values were significantly different across different tree species. Furthermore, glomalin accumulation was also greater below the canopy of these tree species than in the rest of the forest, suggesting glomalin export from epiphytic soils onto the forest floor. These patterns of accumulation of glomalin below canopy trees were also observed in trees isolated in pastures and tracked the stocks of fine roots and soil C and N. The implications of this novel pathway of mycorrhizal contribution to soil heterogeneity and C and N cycling are discussed.