Seed viability, spikelet dispersal, seed banks and seed storage requirements for native and invasive cordgrasses (genus Spartina) in Southwest Iberian Peninsula

Authors: INFANTE-IZQUIERDO, MARIA - Universidad De Huelva; ROMERO-MARTIN, RUTH - Universidad De Huelva; CASTILLO, JESUS - University Of Seville; Grewell, Brenda; SORIANO, JESUS - Universidad De Huelva; NIEVA, F. JAVIER - Universidad De Huelva; MUNOZ-RODRIGUEZ, ADOLFO - Universidad De Huelva

Submitted to: Wetlands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/22/2022
Publication Date: 1/10/2023
Citation: Infante-Izquierdo, M.D., Romero-Martin, R., Castillo, J.M., Grewell, B.J., Soriano, J.J., Nieva, F.J., Munoz-Rodriguez, A.F. 2023. Seed viability, spikelet dispersal, seed banks and seed storage requirements for native and invasive cordgrasses (genus Spartina) in Southwest Iberian Peninsula. Wetlands. 43. Article 8. https://doi.org/10.1007/s13157-022-01655-2.
DOI: https://doi.org/10.1007/s13157-022-01655-2

Interpretive Summary: Spartina cordgrass species have successfully invaded coastal wetlands of several continents, including the western US and Europe, where they have displaced native vegetation, and negatively altered ecosystem processes and services provided by native vegetation. Understanding the mode of reproduction of invasive plants is critical to understanding how an invasive species spreads and persists, and informs management approaches. In the case of sexual reproduction by seed, seedling recruitment is a multi-phase process that can include seed production, seed viability, dispersal, germination, seed bank formation, seedling establishment and survival. Seed banks play an important role in determining the spatial and temporal distribution of halophytes in salt marshes. We tested the ability of native Spartina maritima and invasive S. densiflora spikelets to disperse by flotation on water with different salinity concentrations, and the longevity of spikelets relative to environmental conditions including dry or wet storage at low or moderate temperatures, and aqueous salinity concentrations from fresh to seawater. We quantified pre- and post-dispersal seed production and focal Spartina spp. presence in seed banks located along intertidal gradients within salt marshes at the Gulf of Cádiz (Southwest Iberian Peninsula). S. densiflora spikelets, especially from middle and high elevation marshes, showed greater ability than S. maritima to remain afloat, which suggests this species may disperse over long distances supporting possible colonization of new areas. Wet-stored Spartina seeds were able to maintain viability for months, while seeds under dry storage rapidly lost viability. This decline in viability was most significant for native S. maritima, and for seeds stored at moderate temperatures. Storage of spikelets under wet and cold conditions optimized retention of spikelet viability. Native S. maritima did not establish transient or persistent seed banks, while invasive S. densiflora established transient seed banks mainly at higher marsh elevations. Our results on the dynamics of seed dispersal, seed banks, and seedling recruitment potential of native and invasive congeners provides fundamental knowledge that can be applied for conservation of native S. maritima, management of invasive S. densiflora, and ecological restoration of tidal salt marshes.

Technical Abstract: Seed banks play an important role in determining the spatial and temporal distribution of halophytes in salt marshes. We tested the ability of native Spartina maritima and invasive S. densiflora spikelets to disperse by flotation on water with different salinity concentrations, and the longevity of spikelets relative to environmental conditions including dry or wet storage at low or moderate temperatures, and aqueous salinity concentrations from fresh to seawater. We quantified pre- and post-dispersal seed production and focal Spartina spp. presence in seed banks located along intertidal gradients within salt marshes at the Gulf of Cádiz (Southwest Iberian Peninsula). S. densiflora spikelets, especially from middle and high elevation marshes, showed greater ability than S. maritima to remain afloat, which suggests this species may disperse over long distances supporting possible colonization of new areas. Wet-stored Spartina seeds were able to maintain viability for months, while seeds under dry storage rapidly lost viability. This decline in viability was most significant for native S. maritima, and for seeds stored at moderate temperatures. Storage of spikelets under wet and cold conditions optimized retention of spikelet viability. Native S. maritima did not establish transient or persistent seed banks, while invasive S. densiflora established transient seed banks mainly at higher marsh elevations. Our results on the dynamics of seed dispersal, seed banks, and seedling recruitment potential of native and invasive congeners provides fundamental knowledge that can be applied for conservation of native S. maritima, management of invasive S. densiflora, and ecological restoration of tidal salt marshes.