Carbon for nutrient exchange between Lycopodiella inundata and Mucoromycotina fine root endophytes is unresponsive to high atmospheric CO(2)

Non-vascular plants associating with arbuscular mycorrhizal (AMF) and Mucoromycotina ‘fine root endophyte’ (MFRE) fungi derive greater benefits from their fungal associates under higher atmospheric [CO(2)] (a[CO(2)]) than ambient; however, nothing is known about how changes in a[CO(2)] affect MFRE function in vascular plants. We measured movement of phosphorus (P), nitrogen (N) and carbon (C) between the lycophyte Lycopodiella inundata and Mucoromycotina fine root endophyte fungi using (33)P-orthophosphate, (15) N-ammonium chloride and (14)CO(2) isotope tracers under ambient and elevated a[CO(2)] concentrations of 440 and 800 ppm, respectively. Transfers of (33)P and (15) N from MFRE to plants were unaffected by changes in a[CO(2)]. There was a slight increase in C transfer from plants to MFRE under elevated a[CO(2)]. Our results demonstrate that the exchange of C-for-nutrients between a vascular plant and Mucoromycotina FRE is largely unaffected by changes in a[CO(2)]. Unravelling the role of MFRE in host plant nutrition and potential C-for-N trade changes between symbionts under different abiotic conditions is imperative to further our understanding of the past, present and future roles of plant-fungal symbioses in ecosystems. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00572-021-01033-6.