Simple microplate assays to measure iron mobilization and oxalate secretion by ectomycorrhizal tree roots

The ability of ectomycorrhizal (ECM) fungi to mobilize soil inorganic nutrients has been well documented for a diversity of species. However, most of these studies were performed with tree seedlings or fungal cultures, making them hardly comparable. We propose here three microplate assays to compare iron chelation, free iron uptake and oxalate production by ECMs freshly sampled in mature forest ecosystems. These assays proved to be sensitive enough to detect significant differences between two common ECM types. Lactarius subdulcis was less efficient than Xerocomus sp. for accessing to free or complexed iron, but produced 100 times more oxalate. These preliminary results open the way to study the contribution of ECM communities to nutrient cycling in forest ecosystems.