Above- and belowground phenological complementarity as drivers of biodiversity-ecosystem functioning relationships in experimental tree plantations

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High biodiversity often results in enhanced ecosystem functioning. For grasslands and communities of short lived organisms these positive relationships can be explained by selection effects, facilitation, negative density effects and/or complementarity in resource use. Although positive effects have also been reported for forest ecosystems the mechanistic understanding of biodiversity ecosystem functioning relationships is rather poor in these long lived systems.Our study aims at filling part of this gap by investigating whether temporal complementarity enhances the nutrient uptake in species rich tree plantations compared to monospecific stands.The study is supposed to take part at two experimental sites of the International Diversity Experiment Network with Trees (IDENT), which is part of the global network of tree biodiversity experiments TreeDivNet. The main site will be in Freiburg and a subset of analyses will also take place at a site in Canada to test for the generality of our results.In three work packages we plan to study i) species specific nutrient-tracer uptake rates and functional traits, ii) phenology of nutrient uptake, nutrient status and foliage nutrient content along gradients of tree functional diversity and species richness, and iii) phenology of leaf expansion and abscission, and leaf area index as a function of species richness and functional diversity.Our study should deepen our understanding of the relationship between nutrient uptake and functional traits. Further we will be able to test whether more species rich plantations show a greater continuity of nutrient uptake over time and whether this leads to better nutrient status with higher nutrient uptake rates. Additionally we will investigate whether a greater continuity of canopy development leads to aboveground temporal complementarity in light interception with higher diversity. In a last step we will link aboveground phenology to the phenology of nutrient uptake.The project is planned for three years and should mainly be carried out by a PhD candidate, who will be integrated in the IDENT and TreeDivNet networks.