Nitrogen addition and fungal symbiosis alter early dune plant succession

Abstract

Anthropogenic nitrogen (N) enrichment can have complex effects on plant communities. In low-nutrient, primary successional systems such as sand dunes, N enrichment may alter the trajectory of plant community assembly or the dominance of foundational, ecosystem-engineering plants. Predicting the consequences of N enrichment may be complicated by plant interactions with microbial symbionts because increases in a limiting resource, such as N, could alter the costs and benefits of symbiosis. To evaluate the direct and interactive effects of microbial symbiosis and N addition on plant succession, we established a long-term field experiment in Michigan, USA, manipulating the presence of the symbiotic fungal endophyte Epichloë amarillans in Ammophila breviligulata, a dominant ecosystem-engineering dune grass species. From 2016 to 2020, we implemented N fertilization treatments (control, low, high) in a subset of the long-term experiment. N addition suppressed the accumulation of plant diversity over time mainly by reducing species richness of colonizing plants. However, this suppression occurred only when the endophyte was present in Ammophila . Although Epichloë enhanced Ammophila tiller density over time, N addition did not strongly interact with Epichloë symbiosis to influence vegetative growth of Ammophila . Instead, N addition directly altered plant community composition by increasing the abundance of efficient colonizers, especially C 4 grasses. In conclusion, hidden microbial symbionts can alter the consequences of N enrichment on plant primary succession. Supplementary Information The online version contains supplementary material available at 10.1007/s00442-023-05362-5.