Salinity, Invasive Plants, and the Soil Water Supply

Salinity, Invasive Plants, and the Soil Water Supply by Geno A. Picchioni, New Mexico State University The soil water supply is the hidden but indispensable component of our water budget. In the southwestern U.S., long-term drought, soil salinity, and land-use intensification have increased the risk of invasive plants that cause economic and environmental harm to ecosystems, including the alteration of the soil water supply. Preventing the spread of invasive plants by predictive and preventative practices is considered to be the most economically and environmentally viable approach for control, but the approach is hindered by limited ability to forecast early stages of plant invasions. There is growing appreciation for the role of salinity in regulating plant species populations on semiarid lands, but research is lacking to address this hypothesis. Better understanding of the relationship between salinity and the spread of invasive plants could fill hard data gaps in the literature and have a positive influence on land and water management decisions for rangelands, riparian zones, grazing, crops, dairies, and the oil and gas industry. We have investigated the salinity responses of a unique plant taxon, Lepidium, in greenhouse and growth chamber experiments. Two member species, L. latifolium (perennial pepperweed) and L. draba (white top), have earned their reputations as alien aggressive invaders throughout much of the western U.S. with anecdotal accounts in the literature classifying them as salt-tolerant. A third species, L. alyssoides (mesa pepperwort), is indigenous to New Mexico and our earlier research revealed its potential to become invasive on salt-affected landscapes. In the current study, the salt tolerance of all three species equaled or exceeded that of salt-tolerant cotton despite their combined leaf sodium (Na) and chloride (Cl) concentrations reaching halophytic proportions of 7% to 13% with no characteristic signs of leaf injury. Species such as those in our study appear to exploit high leaf Na and Cl in ways that other plant species cannot and they shed their high-salt leaf litter to the ground at the expense of the other species to intensify the invasive cycle. By “engineering” a site to fit their needs, salt-tolerant invasive plants can significantly alter vegetation diversity by changing the soil water supply and quality. The broad impact of the findings is in application to the larger diversity of invasive plant 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. The NM WRRI just published a technical completion report of a project by Picchioni, Hooks, Schutte, and Daniel, Drought, Salinity, and Invasive Plants: A New Model for Sustainable Water Management. Click here to view NM WRRI Technical Completion Report No. 368. The project was funded by the NM WRRI and the New Mexico Agricultural Experiment Station Rangeland Ecosystems Program.