Fungal symbiosis alters non-host, community-level plant trait response to N enrichment in a low-nutrient sand dune system

Atmospheric nitrogen (N) enrichment is known to alter plant community trait composition and diversity. Additional research in low-resource environments is needed, however, as plant communities in these systems may respond differently than those where N is less limiting. Further, fungal endophytes, such as the Epichloë group, alter key mechanisms of species coexistence but have yet to be studied for their effects on community-level functional traits under conditions of global change. We studied the effects of N enrichment and the presence of aboveground fungal endophyte Epichloë amarillans (Epichloë hereafter) within the dominant grass species, Ammophila breviligulata (Ammophila hereafter), on community-weighted mean (CWM) traits and trait diversity of colonizing plant species in a long-term experiment of a low-resource coastal dune system. N enrichment at both real-world and high levels increased CWMs of plant size and specific leaf area (SLA) of colonizing species, and high N enrichment initially suppressed trait diversity (FDis). While N enrichment reduced community-level specific root length (SRL), this effect disappeared when Epichloë was present, indicating a predominant role of the fungal endophyte. We found that N enrichment may alter plant functional traits, even in a low-resource habitat, which may increase productivity, alter erosional dynamics, and affect belowground functioning. The presence of a fungal endophyte, however, altered community response to N enrichment treatments in a key root trait indicating that its presence may affect community-level traits and belowground functioning beyond its host species.