Parallel to the leaf economics spectrum that links leaf functional traits to carbon (C) gain and tree performance, a root economics spectrum (RES) is expected to link root traits to water and nutrient uptake and tree growth and survival. Yet recent studies indicate that rather than along a single spectrum, root traits associated with resource uptake are organized in a multidimensional trait space that includes various below-ground strategies that are to date under-explored. Moreover, root traits and tree performance are often linked based on correlations between a single trait and vital rate, whereas tree performance is the net result of simultaneous interactions between multiple traits at the whole-tree rather than at the organ level. We test how root traits relate to tree performance using a mechanistic whole-tree model that explores the impacts of root mass – as an under-explored below-ground strategy – specific root length (SRL; root length per root mass) and root lifespan on tree performance, and validate our results with empirical data. Additionally, recent studies identified mycorrhizal fungi as an important strategy in below-ground trait space, and I will conceptually explore how this novel framework could be incorporated in our whole-tree performance model.
Results/Conclusions
Our work demonstrates that 1) increasing root mass can be an adaptive strategy and relevant functional dimension to explain variation in tree performance across species; 2) our whole-tree approach allows testing the effects of unexplored root traits under conditions that are difficult to attain in the field (e.g. by controlling plant size); 3) combining field data and model output helps to explain which root trait strategies may prevail under which conditions. Our model also permits changing other variables that were held constant in the present study (e.g. resource supply rates or above-ground parameters) and incorporating other traits than those currently tested. For example, mycorrhizal fungi were omitted in our model but may be incorporated based on their C costs and uptake benefits to the host tree; however, this requires more data on the exchange rates of C, water and nutrients between the tree and its fungal friends. This presentation concludes with some perspectives to fuel further discussion on linking new conceptual below-ground trait frameworks.