Facilitated invasion by hybridization of Sarcocornia species in a salt‐marsh succession

Abstract

Summary 1We examined salt marsh development over 17 years (1984)(1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001) in a rapidly accreting, well-drained lagoon of a macrotidal marsh in south-west Spain. Scattered, elevated tussocks of colonizing Spartina maritima expanded radially until they either coalesced or were separated only by narrow drainage channels. We recorded changes in elevation of the tussocks and investigated the cover and biomass of successive species invading them. 2 Sediment accretion produced a mean annual increase in tussock elevation of 3.5 cm. Sarcocornia perennis had begun to invade the raised centres of the tussocks by 1984, subsequently displacing Spartina maritima radially to become dominant by 1990. A hybrid form of Sarcocornia , which appeared on some of the tussocks occupied by S. perennis in 1997, also expanded radially and had achieved dominance on many of the invaded tussocks by 2001, by virtue of its more erect growth form and rapid accumulation of high above-and below-ground biomass. 3Tussocks not yet invaded by the hybrid remain dominated by S. perennis and have maintained sediment accretion rates and redox potentials similar to those that have been invaded. 4 Genetic analysis, using random amplified DNA (RAPD) markers, indicated that the hybrid was a cross between the diploid Sarcocornia perennis (2 n = 18) and the octaploid S. fruticosa (2 n = 72), a high-marsh species, and suggested that each hybrid individual may have resulted from a separate pollination of an indigenous S. perennis plant. 5 Invasion by the new hybrid thus probably occurred as a result of pollen flow from high-marsh S. fruticosa , some 1 km distant, to the stigmas of the established dominant S. perennis . Succession might therefore be facilitated genetically rather than simply by the enhanced sediment accretion, which ameliorated the effects of submersion and low sediment redox potentials that presumably exclude S. fruticosa from lower parts of the marsh.

Cordgrass Biomass in Salt Marshes

“…1000 g DW m -2 in low European salt marshes, however it can vary very much depending on the abiotic environment, increasing to ca. 1500 g DW m -2 (Benito & Onaindia, 1991;Castellanos et al, 1994;Figueroa et al, 2003;Lillebo et al, 2006;Castillo et al, 2008a,b) (Table 1). As we have shown above cordgrass above-ground biomass accumulation depends on clone architecture and shoot morphology.…”

“…Thus, central areas may be colonized by more competitive species that are less tolerant to abiotic stress and that finally displace Spartina out by interspecific competition. For example, S. maritima facilitates the development of ecological succession by ameliorating anoxia at the centre of its tussocks, so other species such as Sarcocornia perennis subspecies perennis, Sarcocornia perennis x fruticosa and Atriplex portulacoides are able to colonize them and outcompete the small cordgrass (Castellanos et al, 1994;Figueroa et al, 2003). Most Spartina species with a "phalanx" growth-form accumulate more above-ground biomass than cordgrass species growing in "guerrilla".…”

“…9400 g DW m -2 in high marshes in Maryland, USA (Michel et al, 2009). S. maritima accumulates in the sediments between 400 and 8700 g DW m -2 at low salt marshes that it usually colonizes (Castellanos et al, 1994;Figueroa et al, 2003;Castillo et al, 2008a;Sousa et al, 2008;Caçador et al, 2009). Spartina below-ground biomass accumulation seemed to be favored by sediment accretion (Castillo et al, 2008a) and cordgrass subterranean biomass influences soil elevation rise by subsurface expansion, organic matter addition and sediment deposit stabilization (Ford et al, 1999;Darby & Turner, 2008a).…”

“…Thus, Spartina biomass influences on the carbon content of marsh sediments (Tanner et al, 2010), the marsh carbon stock (Wieski et al, 2010), marsh methane emissions (Cheng et al, 2010), salt marsh microbial community (First & Hollibaugh, 2010;Lyons et al, 2010), grazing (Burlakova et al, 2009), sediment dynamic (Neumeier & Ciavola, 2004;Salgueiro & Cacador, 2007;Li & Yang, 2009), etc. Cordgrass biomass affects the emergent of the habitat structure, facilitating succession development by providing a base for habitat development (Castellanos et al, 1994;Figueroa et al, 2003;Proffitt et al, 2005;Castillo et al, 2008b). For example, S. maritima in European low salt marshes, S. alterniflora in western Atlantic low salt marshes and S. foliosa in Californian low salt marshes are important pioneers and ecosystem autogenic engineers (Castellanos et al, 1994;Castillo et al, 2000;Proffitt et al, 2005).…”

Scale‐Dependent Inhibition Drives Regular Tussock Spacing in a Freshwater Marsh

“…This stimulates sediment capture and retention, leading to the formation of a small mound on which plant growth is focused. In some wetland systems, mounding has been shown to lead to more benign environmental conditions that promote plant growth (Figueroa et al 2003;Fogel et al 2004;Ervin 2005). In tidal freshwater marshes, C. stricta appears less dependent on mounding for evading waterlogging, at least in developed marshes, and instead benefits from growing on top of mounds that provide refuge from small mammalian herbivores that forage in intertussock areas (Crain and Bertness 2005).…”