Impacts of ectomycorrhizal forest change on nutrient cycling, forest resilience, and ecosystem services.

At a time when we count on northern hemisphere forests to mitigate global atmospheric change, European forests are showing deteriorating aboveground nutritional trends without a mechanistic, causal explanation. The increasingly recognized roles of ectomycorrhizal (EM) fungi in global carbon (C), nitrogen (N), and phosphorus (P) cycling mean there is a need to understand dynamics in changing EM forests, particularly at large scales over time. Achieving this requires integrating soil microbial biology with long-term forest monitoring, and a fundamental distributional, temporal, and mechanistic understanding of key soil organisms and the plasticity of their traits across gradients. We postulate that changing abundances of ectomycorrhizas with different capabilities for delivering mineral nutrients from soil to trees, and for storing or releasing soil C, can explain what is happening with forest nutrition, and thus should be included in future models of forest nutrient cycling, above and belowground. Here, we discuss the state-of-the-art regarding data needs, focussing on environmental change, large-scale spatial and temporal dynamics, experimentation, modelling, and monitoring. Linking understanding of tree nutritional status with the potential of forests to cope with environmental change, for instance, anthropogenic C and N fertilization of the biosphere leading to P limitation, holds significant potential to inform management and policy of forests and soils for promoting resilient ecosystems.