Phenotypic plasticity of invasive Spartina densiflora (Poaceae) along a broad latitudinal gradient on the Pacific Coast of North America

Authors: CASTILLO, JESUS - University Of Sevilla; Grewell, Brenda; PICKART, ANDREA - Us Fish And Wildlife Service; BORTOLUS, ALEJANDRO - Centro Nacional Patagonico, Unidad De Investigacio´n De Ecologi´a Terrestre; PENA, C. - University Of Sevilla; FIGUERORA, MANUEL - University Of Sevilla; SYTSMA, MARK - Portland State University

Submitted to: American Journal of Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2014
Publication Date: 3/7/2014
Citation: Castillo, J.M., Grewell, B.J., Pickart, A., Bortolus, A., Pena, C., Figuerora, M.E., Sytsma, M.D. 2014. Phenotypic plasticity of invasive Spartina densiflora (Poaceae) along a broad latitudinal gradient on the Pacific Coast of North America. American Journal of Botany. 101(3):448-458.

Interpretive Summary: Global climate change will affect exotic plant invasions, and it is important to link functional trait-based responses of invaders to environmental changes to improve our understanding of mechanisms that promote invasiveness, predict future invasions, forecast changes in the distribution of alien species, and manage those at hand. Plant species that successfully invade novel habitats beyond their native range are thought to have broad ecological amplitudes and/or physiological tolerances to environmental change. Phenotypic acclimation of individual plants and genetic differentiation by natural selection within invasive populations are two potential mechanisms that may confer fitness advantages and allow plants to cope with environmental variation. A better understanding of the role of phenotypic plasticity of invasive plants in response to environmental variation will also improve our ability to manage weed invasions and improve conservation efforts in natural landscapes. The invasion of S. densiflora across a wide latitudinal gradient from California (USA) to British Columbia (Canada) provides a natural model system to study the potential mechanisms underlying the response of invasive populations to substantial variation in climate and other environmental variables. Towards this end, we examined the phenotypic plasticity of Spartina densiflora along estuarine and continental scale climate gradients. Our results show that key foliar traits varied widely among populations of S. densiflora, and the observed differences were related to variation in physico-chemical characteristics of rootzone sediments, and climatic conditions that varied with latitude. Most foliar traits measured in the field were lower than would be expected under ideal growing conditions, suggesting this invasive species can colonize and persist in suboptimal conditions and will continue to spread under climatic change conditions.

Technical Abstract: We examined morphological and physiological leaf traits of Spartina densiflora plants in populations from invaded estuarine sites across broad latitudinal and climate gradients along the Pacific west coast of North America, and in favourable conditions in a common garden experiment. We hypothesized that S. densiflora would show different foliar responses to environmental changes based mainly on phenotypic plasticity, rather than on genetic differentiation. Our results show that key foliar traits varied widely among populations of S. densiflora, and the observed differences were related to variation in physico-chemical characteristics of rootzone sediments, and climatic conditions that varied with latitude. Most foliar traits measured in the field were lower than would be expected under ideal growing conditions, suggesting this invasive species can colonize and persist in suboptimal conditions. Photosynthetic pigment concentrations at higher latitudes, coinciding with lower radiation, were lower than those observed at lower latitudes. Photosynthetic pigment concentrations of plants in field sites were lower at higher latitudes than those measured in the common garden, suggesting the quality of solar radiation may limit concentrations at higher latitudes. Foliar responses to sediment hypoxic conditions included greater leaf rolling reduced leaf lengths, and lower chlorophyll and higher C concentrations in leaf tissue. Carotenoid ratios and reduced N in leaves were responses to sediment salinity. Our results suggest the variation of foliar traits we observed with environmental variation are a plastic phenotypic response of S. densiflora since nearly all interpopulation differences recorded in the field disappeared when plants were grown in common garden conditions.