Fig. 1

Synthetic representation of the causal relationships in an ectomycorrhizal forest ecosystem (the circled numbers refer to the bold numbers in the legend). Because ECM fungi have diverse nutritional and ecological requirements, the taxonomical structure of the ECM community is impacted by tree phenology (1 seasonal presence or absence of functional leaves, bud break, leaf senescence, periods of shoot elongation, root growth or cambium activity, carbon allocation patterns, developing organs as carbon sink, etc.); photosynthetic efficiency (2 quantity of available photosynthates); tree nutritional status (3 water, phosphorus, nitrogen contents of the root tissues); and soil properties (4 mineral composition and quality of the organic matter). The functional structure of the ECM community first depends on its taxonomical structure (5) because the different symbionts display different profiles of potential activities, but also on the physicochemical properties of the soil (6) and on the availability of nutrients (9), which is in turn determined by the soil properties (7) and by the functional structure of the ECM community itself (8 mineral solubilization, enzymatic degradation of organic matter). Then, the pool of nutrients mobilized by the ECM community directly determines the mineral nutrition of the tree (10), which in turn controls the efficiency of photosynthesis (11), closing the whole feed back loop (from Courty et al. 2010)