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

高生物多样性往往会增强生态系统的功能。对于草地和短命生物群落，这种正向关系可以通过选择效应、促进效应、负密度效应和/或资源利用的互补性来解释。虽然对森林生态系统的积极影响也有报道，但在这些长期生存的系统中，对生物多样性生态系统功能关系的机制了解相当不足。我们的研究旨在通过调查与单一物种相比，时间互补是否提高物种丰富的树木人工林的养分吸收来填补这一空白。本研究应参加国际树木多样性实验网络(IDENT)的两个实验点，该网络是全球树木生物多样性实验网络TreeDivNet的一部分。主要地点将在弗莱堡，部分分析也将在加拿大的一个地点进行，以测试我们结果的一般性。我们计划在三个工作包中研究i)物种特定的营养示踪剂吸收速率和功能性状，ii)养分吸收、营养状况和叶片养分含量随树木功能多样性和物种丰富度梯度的物候学，以及iii)叶展开和脱落的物候学，以及叶面积指数作为物种丰富度和功能多样性的函数。我们的研究应该加深我们对养分吸收和功能性状之间关系的理解。此外，我们将能够测试更多物种丰富的种植园是否随着时间的推移表现出更大的养分吸收连续性，以及这是否会导致更好的营养状况和更高的养分吸收速率。此外，我们还将研究冠层发育的更大连续性是否会导致具有更高多样性的光截获的地上时间互补性。在最后一步中，我们将把地上物候与养分吸收的物候联系起来。该项目计划三年，主要由一名博士生实施，他将被整合到IDENT和TreeDivNet网络中。

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.