LAUSR

Abstract Non-native plant species can alter soil communities, which can lead to changes in their ecosystem functioning and facilitate invasive plant spread. In this study, we asked whether abundance, composition, or function of free-living soil nematode communities differed in association with two dune building grass species in US Pacific Northwest coastal dunes. In 2016, we surveyed soil nematode communities along foredune profiles at six sites in Oregon and Washington, USA, where the non-native beach grass Ammophila breviligulata co-occurred with the native dune grass Elymus mollis. We also measured plant-associated factors that might influence nematode communities, including plant tissue nitrogen, arbuscular mycorrhizal associations, litter production, and plant community diversity associated with the two grass species across the foredune profile. Elymus mollis plots had over twice as many nematodes on average as A. breviligulata plots and were also associated with a higher nematode enrichment index, especially on dune heels. This is possibly explained by higher percent leaf nitrogen content in E. mollis. Subtle differences in nematode community composition and plant tissue nitrogen between the two grass species indicate that A. breviligulata may be altering nutrient cycling across the dune profile, which could explain the arrested succession associated with this species on back dunes. However, overall, nematode communities shifted more in response to foredune cross-shore position and stabilization as opposed to changes in vegetation.