In the semiarid southwestern United States, long-term drought, soil salinity, and land-use intensification have increased the risk of invasive plants that threatens landscape biodiversity. Soil-related factors that regulate plant invasions are not adequately known. We evaluated the salinity responses of three invasive plant species during a 3-mo plant growth period in a greenhouse and during a 2-wk seed germination study in the laboratory. The species included the indigenous Lepidium alyssoides A. Gray var. alyssoides (mesa pepperwort) and the exotic, invasive L. draba L. (whitetop) and L. latifolium L. (perennial pepperweed). A NaCl solution at -0.2 MPa reduced germination of L. alyssoides by ≈20% and had no effect on germination of L. draba and L. latifolium, merely delaying their mean germination time by a day or less. Reductions in seedling dry matter production and evapotranspiration (ET) were observed following irrigation with NaCl solutions at -0.1 MPa and -0.2 MPa. However, on the basis of ET and total plant dry matter production under common experimental conditions, the salt resistance of these species greatly exceeded that of salt sensitive bean (Phaseolus vulgaris L.) and equaled or exceeded that of salt-resistant cotton (Gossypium hirsutum L.). Below-ground propagating structures giving rise to clonal shoots were observed for all Lepidium spp., consistent with other reports. The results indicate that vegetative propagule pressure and relatively high resistance to salinity at germination and seedling growth stages could contribute to the invasiveness of these species under saline conditions. A broader impact of the findings is in their application to the larger diversity of invasive species to aid in the understanding of soil salinity and how it may govern plant invasions. This dataset could improve risk assessment measures to favor biodiversity in rangelands and natural ecosystems of semiarid regions.
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Vol. 71 • No. 4