Seedling Germination and Salinity Tolerance in cordgrass Spartina foliosa and Spartina alterniflora x foliosa Hybrids Courtney W Davis Abstract An exotic cordgrass species Spartina alterniflora hybridized with the native cordgrass S foliosa after its 1970s introduction into the San Francisco CA estuary Hybrids are spreading rapidly throughout the Bay potentially altering the estuary ecosystem which supports more than a million shorebirds including the endangered California Clapper Rail Previous studies were conducted on the salinity tolerance of the plants in both individual species and hybrids between the two however the salinity tolerance of the seeds had not been previously studied The goal of this study was to determine the salinity tolerance of the seeds in both the native and hybrid species Twelve hybrid cordgrass plants were selected based on their experimentally determined salinity tolerance assessed using end of experiment biomass conduced at UC Davis their ability to produce seed and their genetic background ranging from 0 to 93 S alterniflora Two S foliosa individuals were collected from a restored tidal marsh in San Francisco Bay genetic analysis indicated was uninvaded by hybrids No genetic analysis was preformed on the seeds There were 2 pre germination treatments low and high salinity and 3 germination treatments low medium high salinity 6 treatments Results show that the pre germination environments do not have an effect on the seeds The germination environments do however affect the seeds and an increase in salinity leads to a decrease in germination Parent clones also affect the salinity tolerance of the seeds These results could have enormous implications for the future of native S foliosa and the species that it supports Introduction It has been widely recognized that introduced species can pose threats to native ecosystems and alter them dramatically This has been documented many times throughout history For example Lantana depressa an endemic plant to Dade County Florida is hybridizing with the introduced species common in southern gardens L camara the hybrids combine the vigor of the alien with the local adaptations of the native resulting in a loss of native species Levin 2002 The most numerous exotic spreading rapidly throughout the San Francisco estuary is hybrids between Spartina alterniflora Smooth cordgrass and Spartina foliosa California cordgrass Ayres et al 2004 These hybrids have the potential to permanently alter the estuary ecosystem Callaway and Josselyn 1992 The salt marshes in the San Francisco Bay supports a variety of species including endangered species such as the California clapper rail Rallus longirostris obsoletus and the salt marsh harvest mouse Rerthrodontomys raviventris Over 1 million migratory shorebirds on the Pacific Flyway Route pass through the San Francisco estuary annually feeding on the invertebrate fauna of unvegetated mudflats during low tide Hybridization is perhaps an equal or greater threat to S foliosa than is ecological competition with S alterniflora Ayres et al 1999 S foliosa is a native perennial salt marsh grass found from Bodega Bay CA to Baja Mexico San Francisco Estuary Invasive Spartina Project Page 2003 elect comm It is anticipated that if the hybrid population is left unchecked S foliosa will become the first naturally dominant plant species to go extinct in its own ecosystem since the passage of the Endangered Species Act in 1973 San Francisco Estuary Invasive Spartina Project Page 2003 elect comm Spartina alterniflora also a perennial cordgrass is native to the eastern and gulf coasts of the USA and was introduced in the San Francisco Bay in the mid 1970s Ayres et al 1999 Previous studies have shown that S alterniflora can grow in elevational zones both higher and lower 9 20cm than the native S foliosa Callaway and Josselyn 1992 However S alterniflora x foliosa hybrids pose a greater threat to the San Francisco Bay than S alterniflora because they have greater morphological and reproductive vigor than either parental species Ayres et al 2003 Spartina alterniflora x foliosa hybrid plants coalesce while also accreting and stabilizing sediment around them converting tidal mudflats to cordgrass meadows Daehler and Strong 1996 This process increases the elevation of the mudflat for further colonization San Francisco Estuary Invasive Spartina Project Page 2003 elect comm Colonization alters marsh hydrology and channel habitat dramatically while increasing the risk of upland flooding and decreasing the area of mudflats used by foraging birds Callaway and Josselyn 1992 Genetically tested hybrid plants showed a wide range 10ppt 40ppt of tolerance to salinity in a previously conducted common greenhouse experiment Pekenham Walsh 2003 The purpose of this experiment is to determine if hybrid seeds also show a wide range of salinity tolerances however no genetic analysis was conducted on the seeds Seeds are carried by tides and these tides have the potential to spread the invasion throughout the San Francisco Bay and outside of the estuary Ayres et al 2003 Seeds that can germinate in higher salinities will have an advantage over those less tolerant to salinity because they can establish at higher elevations D A 2003 elect comm I hypothesize that seeds with a low tolerance to salinity will be those of S foliosa due to its restriction in tidal marshes to lower salinity sites and its poor growth in high salinity in the greenhouse relative to several hybrids I also hypothesis that a subset of hybrid plants will produce seeds with higher salinity tolerance D A 2003 elect comm This experiment tests whether the tolerance of salinity ranging from 10ppt to 40ppt in established plants is correlated with the salinity tolerance of their progeny and whether there is interaction between the pre and germination salinity environments D A 2003 elect comm Methods Data collection Seeds were collected yielding varying seed sets Table 1 in November 2003 from twelve in situ Spartina alterniflora x foliosa hybrid plants located at Cogswell Marsh in Hayward CA and two in situ S foliosa plants at Mt View tidal marsh which is uninvaded by hybrids at Shoreline Park Mt View CA Clone ID C1 5 C2 11 C2 13 C2 5 C2 6 C2 8 C3 1 C3 13 C3 4 C3 5 C3 7 C3 8 SF 1 SF 2 A 146 66 53 46 146 88 118 58 38 84 92 68 228 162 B 98 60 77 96 86 92 40 30 42 76 153 56 184 220 C 126 64 47 64 183 116 124 30 58 96 81 62 228 164 Table 1 Seed Set Data C S alterniflora x
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