Fine roots play a significant role in plant and ecosystem respiration (RS); therefore, understanding factors controlling that process is important both to advancing understanding and potentially in modelling carbon (C) budgets. However, very little is known about the extent to which ectomycorrhizal (ECM) identity may influence RS or the underlying chemistry that may determine those rates. In order to test these relationships, we examined RS, measured as O 2 consumption, of first-order ECM root

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... ips of Pinus sylvestris L. and Quercus robur L. saplings in relation to their ECM fungal symbionts and associated nitrogen (N), C and non-structural carbohydrate concentrations. Roots of P. sylvestris were colonized by Rhizopogon roseolus, Tuber sp. 1 and an unknown species of Pezizales. Fungal species colonizing Q. robur roots were Hebeloma sp., Tuber sp. 2 and one unidentified ECM fungus described as Tuber-like based on ECM morphology. ECM RS rates for different host species were significantly different and more than 97% of the variation in RS within a host species was explained by ECM root tip N concentrations. This may indicate that some of the variability in fine root RS-N relationships observed between and within different host species or their functional groups may be related to intraspecific host species differences in root tip N concentration among ECM fungal associates.