Carbon for nutrient exchange between Lycopodiella inundata and Mucoromycotina fine root endophytes is unresponsive to high atmospheric CO2

Abstract

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 [CO₂] (a[CO₂]) than ambient; however, nothing is known about how changes in a[CO₂] 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 ³³P-orthophosphate, ¹⁵ N-ammonium chloride and ¹⁴CO₂ isotope tracers under ambient and elevated a[CO₂] concentrations of 440 and 800 ppm, respectively. Transfers of ³³P and ¹⁵ N from MFRE to plants were unaffected by changes in a[CO₂]. There was a slight increase in C transfer from plants to MFRE under elevated a[CO₂]. Our results demonstrate that the exchange of C-for-nutrients between a vascular plant and Mucoromycotina FRE is largely unaffected by changes in a[CO₂]. 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.