Above- and belowground plant complementarity

• Applicants: Professorin Dr. Liesje Mommer; Professorin Dr. Alexandra Weigelt
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: from 2016 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 163658437

Increasing plant diversity enhances many aspects of ecosystem functioning. The increased performance of communities with higher diversity is thought to originate from two distinct classes of mechanisms: (1) complementarity effects and (2) sampling effects, but current knowledge suggests that complementarity is the dominating force driving biodiversity ecosystem function (BEF) relationships. The detection and quantification of complementarity is challenging, especially belowground. Direct, mechanistic approaches rely on the use of isotopically labelled compounds to measure nutrient uptake or on measurements of space exploitation above- or belowground. Indirect, correlative approaches attempt to link plant traits as proxies of niche definition to plant performance or compare species performance in monoculture and mixtures. So far, these approaches have mainly been used in isolation and yielded mixed results. Here, we argue that a synthesis and comparison of these approaches is urgently needed to answer a longstanding, but still unanswered question in ecology: what is the relative importance of complementary use of different resources for the BEF relationship? We aim to integrate the existing evidence from direct and indirect approaches and explore, for the first time, a comprehensive picture of resource complementarity in plants of grassland ecosystems. So far, results from direct approaches support aboveground complementarity for light while evidence for belowground resource complementarity is inconclusive. In work package 1 (WP 1) we aim to comprehensively synthesize all evidence for direct complementarity measurements from the Jena Experiment as well as data from other biodiversity experiments. We will organize an international workshop to yield a comprehensive review and a meta-analysis of this data. Indirect evidence for complementarity driving the BEF relationship is more often found than direct evidence, but is limited primarily to aboveground biomass and aboveground traits. In work package 2 (WP 2) we will compile the largest available trait dataset for species of the Jena Experiment, including many root traits, and make it publicly available. With this dataset, we will systematically screen the importance of community weighted means (CWM related to selection effects) or functional diversity of traits (FD related to complementarity effects) for a large number functions in the context of resource complementarity. In a final step (WP 3), we will combine these results to finally analyse the relative importance of above- and belowground resource complementarity measured via direct or indirect approaches in the Jena Experiment. Using path analysis, the third WP will reveal if resource complementarity is indeed an important mechanism of BEF relationships and whether or not its importance depends on the ecosystem function under study.

• DFG Programme: Research Units
• Subproject of: FOR 1451: Exploring Mechanisms Underlying the Relationship between Biodiversity and Ecosystem Functioning
• International Connection: France, Netherlands, Switzerland
• Co-Investigators: Professorin Dr. Nina Buchmann; Professorin Dr. Gerlinde B. de Deyn; Professor Dr. Arthur Gessler; Professor Dr. Hans de Kroon; Privatdozent Alexandru Milcu, Ph.D.; Privatdozentin Dr. Christiane Roscher; Dr. Jasper van Ruijven; Professor Dr. Michael Scherer-Lorenzen; Professor Dr. Christian Wirth