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In forest ecosystems, ectomycorrhizal (ECM) fungi are important for plant growth and soil biogeochemical processes. The biochemical composition of ECM mycelium is an important fungal effect trait with consequences for its decomposition rate, and consequently on soil carbon pools and plant nutrition. Although the link between ECM fungi and leaf litter-released nutrients is well known, the response of ECM fungal biochemical composition to different leaf litter species remains poorly understood. To determine how leaf litter quality influences ECM fungi's biochemical profiles, we planted young beech trees in an oak forest and replaced the natural leaf litter with that of European beech (Fagus sylvatica), ash (Fraxinus excelsior), maple (Acer pseudoplatanus), or lime (Tilia cordata). We assessed the biochemical profiles of ECM root tips colonized by common fungal taxa in temperate forests (i.e., Cenococcum geophilum, Inocybe sp., and Lactarius subdulcis), using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR). ECM fungal biochemical composition changed with leaf litter species. Changes were apparent in the infrared absorption bands assigned to functional groups of lipids, amides, and carbohydrates. C. geophilum and L. subdulcis exhibited large spectral differences corresponding to the initial pattern of leaf litter chemical composition between samples collected in the beech and ash leaf litter treatments. In contrast, Inocybe sp. was influenced by lime, but with no differences between samples from ash or beech leaf litter treatments. Although the spectral bands affected by leaf litter type differed among ECM fungi, they were mainly related to amides, indicating a dynamic response of the fungal proteome to soil nutritional changes. Overall, the results indicate that the biochemical response of ECM fungi to leaf litter species varies among ECM fungal species and suggests that the biochemical composition of ECM mycelium is a fungal response trait, sensitive to environmental changes such as shifts in leaf litter species.

Litter decomposition is strongly controlled by litter quality, but the composition of litter mixtures and potential interactions with live plants through root activity may also influence decomposers. In a greenhouse experiment in French Guiana we studied the combined effects of the presence of tropical tree seedlings and of distinct litter composition on mass and nitrogen (N) loss from decomposing litter and on microbial biomass. Different litter mixtures decomposed for 435 days in pots filled with sand and containing an individual seedling from one of four different tree species. We found both additive and negative non-additive effects (NAE) of litter mixing on mass loss, whereas N loss showed negative and positive NAE of litter mixing. If litter from the two tree species, Platonia insignis and Goupia glabra were present, litter mixtures showed more positive and more negative NAE on N loss, respectively. Overall, decomposition, and in particular non-additive effects, were only weakly affected by the presence of tree seedlings. Litter mass loss weakly yet significantly decreased with increasing fine root biomass in presence of Goupia seedlings, but not in the presence of seedlings of any other tree species. Our results showed strong litter composition effects and also clear, mostly negative, non-additive effects on mass loss and N loss. Species identity of tree seedlings can modify litter decomposition, but these live plant effects remain quantitatively inferior to litter composition effects. [ABSTRACT FROM AUTHOR]