Variation in tussock traits of the invasive cordgrass Spartina densiflora along the Pacific Coast of North America

Authors: CASTILLO, JESUS - University Of Sevilla; Grewell, Brenda; PICKART, ANDREA - Us Fish And Wildlife Service; FIGUERORA, MANUAL - University Of Sevilla; SYTSMA, MARK - Portland State University

Submitted to: Biological Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/25/2015
Publication Date: 7/17/2016
Citation: Castillo, J.M., Grewell, B.J., Pickart, A., Figuerora, M.E., Sytsma, M.D. 2016. Variation in tussock traits of the invasive cordgrass Spartina densiflora along the Pacific Coast of North America. Biological Invasions. 18:2159-2174.

Interpretive Summary: Spartina densiflora (austral cordgrass), native to southern South America, is an aggressive grass species that has invaded estuarine ecosystems in North America and Europe. 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. It is important to link functional trait-based responses of invaders to environmental changes to improve our understanding of mechanisms that promote invasiveness. This manuscript evaluates 17 functional traits of many individual Spartina densiflora tussocks from five populations distributed along a broad latitudinal and climate gradient from the central and northern Pacific Coast of North America. We analyzed relationships between 13 climate, hydrologic and sediment variables measured at each population site and the resultant tussock architecture traits of the tussocks. We compared architecture traits growing in a wide range of field conditions, and we also grew plants from the each of the studied field populations in a common garden experiment conducted in a greenhouse. Our results suggest plants from these populations are able to adjust key functional tussock traits across a wide latitudinal gradient in response to widely variable climate (specifically, air temperature) and sediment conditions. These results are important for invasive species risk assessment and management planning in the context of climate change.

Technical Abstract: Some introduced species rapidly spread to cover large novel habitats beyond their native range mediated by a high degree of phenotypic plasticity and/or rapid evolutionary responses. In this context, clonality has been described as a significant factor contributing to invasiveness. We studied the abiotic environment and the responses of different tussock architecture traits of the invasive cordgrass Spartina densiflora Brongn. (Poaceae) in salt marshes across a wide latitudinal gradient from California (USA) to British Columbia (Canada) and in a common garden experiment, a model system for an integrated study of the potential mechanisms underlying the response of invasive populations to changes in environmental conditions. Our results show that S. densiflora is able to adjust though phenotypical plasticity key functional tussock traits, such as shoot density and height and above- and below-ground biomass allocation patterns, in response to widely variable climate (specifically, air temperature and the duration of the growing season) and sediment conditions (specifically, texture and hypoxia). Root biomass increased in coarser sediments, showing the opposite response than rhizomes that were more abundant in more fine sediments. Above-ground biomass and leaf area index increased mainly with air temperature during summer and more robust (taller and wider) shoots were recorded growing on more oxygenated sediments. In view of our results, S. densiflora appears to be a halophyte with a high degree of phenotypic plasticity that would enable it to respond successfully to changes in the abiotic conditions of salt marshes driven by global climate change, such as increasing salinity and temperatures.