There are no trends in germination and seedling growth in a temperate native grassland along an invasion gradient because of opposing plant-soil feedbacks

Abstract Background and Aims Invasive exotic plant species change biotic plant-soil feedback but the effects on abiotic plant-soil feedback is less well understood. This study investigates biotic and abiotic legacies along an invasion gradient on germination and growth of several native and one exotic species in a Temperate Native Grassland. Methods Topsoil cores were extracted from inter-tussock spaces in seven grassland sites varying in exotic plant species richness. Half the cores were sterilised, and to half the live- and half the sterile-cores, a microbial wash was added. Five native forbs and one invasive exotic grass were sown apart in each core. Non-destructive and destructive measurements were made. Results Removal of soil biota by sterilisation improved germination of two native forbs and the microbial wash influenced germination of two species but not seedling growth of any species. Growth of native forbs in sterile cores increased along the invasion gradient, whereas growth of native forbs in live cores was the same along the gradient. In the live cores the increases in the abiotic plant-soil feedback were offset by reduction in the biotic plant-soil feedback. Biotic plant-soil feedback negatively and similarly affected growth of the invasive grass species at all sites. Conclusion This study demonstrates that both biotic and abiotic plant-soil feedback in native grassland continue to be changed by ongoing invasion and the changes have a minor influence on germination and a consistent but opposing influence on growth of native species.