Designing a Robust and Versatile System to Investigate Nutrient Exchange in, and Partitioning by, Mycorrhiza (Populus x canesces x Paxillus involutus) Under Axenic or Greenhouse Conditions Katharina Schreider 1 * , Jens Boy 1 , Leopold Sauheitl 1 , Aline Fernandes Figueiredo 2 , Alberto Andrino 1 and Georg Guggenberger 1 1 Institute of Soil Science, Leibniz Universität Hannover, Hannover, Germany, 2 Institute of Physiology and Cell Biology, Tierärztliche Hochschule Hannover, Hannover, Germany Phosphorus (P) bioavailability affects plant nutrition. P can be present in soils in different chemical forms that are not available for direct plant uptake and have to be acquired by different mechanisms, representing different resource niches. These mechanisms, of which many seem to be attributed to mycorrhiza, likely influence the diversity and stability of plant communities in natural ecosystems, as they also might help to overcome a future shortage of P supply in agro-ecosystems. In order to understand the mechanisms of P acquisition, the associated carbon costs, and the resource partitioning by mycorrhizal fungi, the ecosystem situation has to be mimicked in smaller scaled experiments. Here, different experimental setups are evaluated using plantlets of Populus x canescens and its functional ectomycorrhizal (ECM) fungus Paxillus involututs strain MAJ. To investigate resource partitioning involving mycorrhizae, the protocols of this study describe preparation of an in vitro and a rhizotrone culture systems for studies under axenic conditions as well as a mesocosm culture system for greenhouse conditions. We also describe the construction of separate compartments containing nutrients and excluding plant roots as well as the progress that has been made in in vitro propagation of plant and ECM fungal material. The practical experience made in our Frontiers in Fungal Biology | www.frontiersin.org June 2022 | Volume 3 | Article 907563 1 Edited by: Everlon Cid Rigobelo, São Paulo State University, Brazil Reviewed by: Rodica Pena, University of Reading, United Kingdom Diego Zied, São Paulo State University, Brazil *Correspondence: Katharina Schreider schreider@ifbk.uni-hannover.de Specialty section: This article was submitted to Fungi-Plant Interactions, a section of the journal Frontiers in Fungal Biology Received: 29 March 2022 Accepted: 16 May 2022 Published: 17 June 2022 Citation: Schreider K, Boy J, Sauheitl L, Figueiredo AF, Andrino A and Guggenberger G (2022) Designing a Robust and Versatile System to Investigate Nutrient Exchange in, and Partitioning by, Mycorrhiza (Populus x canesces x Paxillus involutus) Under Axenic or Greenhouse Conditions. Front. Fungal Bio. 3:907563. doi: 10.3389/ffunb.2022.907563 METHODS published: 17 June 2022 doi: 10.3389/ffunb.2022.907563