DROUGHT, SALINITY, AND INVASIVE PLANTS: A NEW MODEL FOR SUSTAINABLE WATER MANAGEMENT
Geno A. Picchioni, Triston N. Hooks, Brian J. Schutte and David L. Daniel
Long-term drought, soil salinity, and land-use intensification have increased the risk of invasive plants in the semiarid southwestern United States. However, soil-related factors that regulate plant invasions are not adequately known. We evaluated the salinity responses of three invasive plant species during a three-month seedling growth period in a greenhouse, and a two-week seed germination period in the laboratory. The species included the indigenous Lepidium alyssoides (mesa pepperwort), and the exotic invasive L. draba (whitetop) and L. latifolium (perennial pepperweed). Significant reductions in seedling growth and evapotranspiration (ET) of three local L. alyssoides populations were largely independent of various isosmotic saline irrigation solutions that included NaCl, Na2SO4, and CaCl2, each at -0.1 MPa and -0.2 MPa (17 to 48 mM depending on salt species and osmotic potential), suggesting that ET and growth were controlled by solution osmotic potential. Based on ET and total dry matter production under similar experimental conditions, the salt tolerance of these species equaled or exceeded that of salt-tolerant cotton (Gossypium hirsutum), despite their combined leaf Na and Cl concentrations of 7% to 13% of dry weight and no characteristic signs of leaf injury. These species appear to exploit high leaf Na and Cl for the maintenance of turgor, and would eventually shed high-salt leaf litter to the ground at the expense of other salt-sensitive species to continue the invasive cycle. A NaCl solution at -0.2 MPa (48 mM) had no effect on germination percentages of L. draba and L. latifolium, rather, it merely delayed their mean germination time by a day or less. Under saline conditions, high germinability and vegetative propagule pressure along with high-salt litter deposition are major factors contributing to the invasiveness of these species, and this report is the first that we are aware to provide a quantitative basis for their invasions. However, the broader impact of this research is in the application to the larger diversity of invasive species to aid in the understanding of factors that govern invasions, to strengthen predictive and preventative measures, and to preserve the quality and supply of soil water in semiarid regions.
Keywords: Lepidium alyssoides, L. draba, L. latifolium, Phaseolus vulgaris, Gossypium hirsutum, sodium, chloride, Chihuahuan Desert, evapotranspiration, soil water, seed germination, anthropogenic disturbance, salinization, wastewater