Liming in a beech forest results in more mineral elements stored in the mantle of Lactarius subdulcis ectomycorrhizas

Liming is a forest practice used to counteract forest decline induced by soil acidification. It consists of direct Ca and Mg input in forest soil and restores tree mineral nutrition, but also causes drastic changes in nutrient availability in soil. Ectomycorrhizal (ECM) fungi significantly contribute in nutrient uptake by trees, and can recover them through organic acid secretion or through enzymatic degradation of organic matter. The symbiotic fungi use their extraradical mycelium for nutrient uptake, and then store them into the ECM mantle. In this study we measured how liming influences element contents in the mantle of Lactarius subdulcis ECMs, an abundant and particularly active in oxalate and laccase secretion in beech stands. For this purpose we used SEM observation coupled with energy- (EDX) and wavelength-dispersive-X-ray microanalyses (WDX). Results showed that ECM mantles of this species presented significantly higher Ca, Mg, Mn, K, Si, Al and Fe contents in limed plots. The nutrient amounts of L. subdulcis ECMs were significantly different between individuals for all the elements, showing a differential storage ability between individuals. The storage role of the ECM mantle can be interpreted in two different ways: i) a detoxification role for Al or heavy metals and ii) an increased potential nutrient resource by the fungus, which can benefit the tree.