Germination Responses of the Invasive Triadica sebifera and Two Co-occurring Native Woody Species to Elevated Salinity Across a Gulf Coast Transition Ecosystem

With sea level rise, coastal ecosystems farther inland are expected to experience extended duration of inundation and elevated salinity. However, the effects of elevated salinity on initial recruitment of native and invasive woody species in coastal ecosystems are poorly understood. We assessed effects of elevated salinity across a range of soil types on germination of the invasive Triadica sebifera and two natives, Baccharis halimifolia and Morella cerifera, using growth chamber and greenhouse experiments. In both studies, germination was compared across four salinity levels (0, 10, 20, and 30 g/l). In the greenhouse, percent germination of these species was also compared across soils spanning the five dominant vegetation zones that define a typical coastal transition ecosystem in coastal Mississippi, USA. Final percent germination of all species decreased with increased salinities in both experiments. In the greenhouse, germination of all species was reduced in soils from the most seaward vegetation zones. Overall, there were species-specific germination responses to salinity treatments and soil types. Of the three species, B. halimifolia was least sensitive to increasing salinity. Germination of the invasive Triadica sebifera did not differ across salinity levels in inland soils, displaying plasticity of germination traits. This plasticity may increase the likelihood of successful germination under some degree of salinity stress, and thereby contribute to the inland spread of T. sebifera along coastal transition ecosystems.