Competition, salinity, and clonal growth in native and introduced irises.
Iris pseudacorus spread rapidly into North America after introduction from Europe in the 1800s and now co-occurs with native I. hexagona in freshwater Louisiana wetlands. Native irises support and interact with multiple trophic levels, whereas I. pseudacorus is classified an invasive pest because it grows aggressively, reduces biodiversity, and displaces native vegetation. Salinity levels are increasing in coastal wetlands worldwide. We examined how salt-stress affects competitive interactions between these conspecifics.



We established a three-way full-factorial common-garden experiment that included species (I. pseudacorus, I. hexagona), competition (no competition, intraspecific competition, and interspecific competition), and salinity (0, 4, 8 parts per thousand NaCl), with six replicates per treatment.



After 18 mo, Iris pseudacorus produced much more biomass than the native species did (F1, 92 = 71.5, P < 0.0001). Interspecific competition did not affect the introduced iris, but biomass of the native was strongly reduced (competition × species interaction: F2, 95 = 76.7, P = 0.002). Salinity significantly reduced biomass of both species (F2, 92 = 21.8, P < 0.0001), with no species × salinity interaction (F2, 84 = 1.85, P = 0.16).



Our results demonstrate that salt stress strongly reduced clonal reproduction in native and introduced irises; however, the introduced iris had a competitive advantage over the native, regardless of environmental salinity levels. Based on patterns in clonal reproduction, the introduced iris could potentially threaten native iris populations. We are currently investigating seed production and mortality during competition and stress because both clonal and sexual reproduction must be considered when predicting long-term population dynamics.
Ecology Center, 703 Thoroughbred Drive, University of Louisiana, Lafayette, Louisiana 70507 USADepartment of Biology, 410 East Saint Mary Blvd., University of Louisiana, Lafayette, Louisiana 70503 USA mop@louisiana.edu.
Susan
S
Mopper
Ecology Center, 703 Thoroughbred Drive, University of Louisiana, Lafayette, Louisiana 70507 USADepartment of Biology, 410 East Saint Mary Blvd., University of Louisiana, Lafayette, Louisiana 70503 USA.
Karen C
KC
Wiens
Ecology Center, 703 Thoroughbred Drive, University of Louisiana, Lafayette, Louisiana 70507 USADepartment of Biology, 410 East Saint Mary Blvd., University of Louisiana, Lafayette, Louisiana 70503 USA.
Greta A
GA
Goranova
D018533:Biomass; D004305:Dose-Response Relationship, Drug; D005618:Fresh Water; D058865:Introduced Species; D031323:Iris Plant / Q000187:drug effects / Q000254:growth & development / Q000502:physiology*; D011157:Population Dynamics; D012100:Reproduction, Asexual / Q000187:drug effects; D054712:Salinity; D012965:Sodium Chloride / Q000494:pharmacology*; D053833:Wetlands
D012965:Sodium Chloride
Iridaceae; Iris hexagona; Iris pseudacorus; clonal reproduction; coastal wetlands; environmental disturbance; interspecific competition; invasive plants; salinity stress