The economic trade-off between root hairs and mycorrhizal extraradical hyphae along a land use gradient (HAIRphae)

• Applicant: Dr. Joana Bergmann
• Subject Area: Ecology and Biodiversity of Plants and Ecosystems
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 432975993

Plant resource economics are classically defined as a spectrum ranging from acquisition to conservation. However, fine roots are still underrepresented in this concept. Recent findings suggest that root traits are multidimensional particularly because of their interaction with soil biota. A trade-off between the investment into root surface and arbuscular mycorrhizal fungal (AMF) surface for nutrient uptake has been hypothesized using specific root length (SRL) as a proxy of root surface maximization. On the other hand, it is well known that root hairs strongly affect phosphorus uptake. Still, they are not included in recent concepts of resource economics. In preliminary greenhouse experiments we found root hair length and incidence to negatively correlate with mycorrhizal colonization. This gradient between a strategy of increasing either root hair surface or the mycorrhizal symbiosis was found to be independent of SRL suggesting that the trade-off contains information disregarded in root economic concepts so far.Acquisitive AMF surface - namely extraradical hyphal length - has been found to increase with land-use intensity, with soil nutrient stoichiometry being a possible environmental driver. Therefore, when studying the complexity of the root-fungal-surface trade-off, field data including soil environmental variation are needed. In this project, I aim to test the concept of a root-fungal-surface trade-off including root hairs and extraradical hyphae for the first time. I will sample single individuals of the most dominant plant species in the field (VIP level) along a land-use gradient. Based on previous results I hypothesize a shift from an investment into root hairs to an extension in extraradical hyphal surface with increasing land use intensity. Due to species overlap between the plots I will also be able to test inter- and intraspecific pattern of variation. The AMF community in the rhizosphere will be analyzed to test if changes in extraradical hyphal length originate from AMF community shifts. In a mechanistic greenhouse experiment the direct effect of soil nutrient stoichiometry will be studied. The AMF community in the rhizosphere and the root compartment will be examined to test plant mediation of fungal community shifts as well as fungal plasticity in allocation to extraradical hyphae. Data will be synthesized with root morphological, anatomical and chemical traits from previous Biodiversity Exploratories projects to integrate the root-fungal-surface trade-off into existing root economic concepts. The framework of the Exploratories will allow me to link this improved understanding of root trait variation to ecosystem processes like plant productivity, nutrient cycling or soil aggregation. This project will enhance our mechanistic understanding of root trait multidimensionality and help to investigate the importance of root traits for predicting plant community and ecosystem changes under increasing land use and global change.

• DFG Programme: Infrastructure Priority Programmes
• Subproject of: SPP 1374: Biodiversity Exploratories