Effects of Salt and Drought Stress on Germination of Non-native Plants in the Salt Marsh to Upland Transition Zone

Non-native plants are often found in the transition between the high salt marsh and upland zones of southern California salt marshes. Although plants in these transition zones experience high levels of abiotic stress associated with high salinity and seasonally variable moisture levels, non-native plants are often able to germinate during brief periods of lowered soil salinity that occur after winter rain. In this study, the germination response of four non-native plants (Glebionis coronaria, Mesembryanthemum crystallinum, Atriplex semibaccata, and Bassia hyssopifolia) was tested in a growth chamber at a range of soil salinity and moisture conditions found within this zone. Glebionis coronaria and Mesembryanthemum crystallinum were restricted to a narrow range of less stressful soil conditions, with successfully germination generally only at soil salinity values of 10ppt or lower, and germination greatly diminished by low moisture levels. Atriplex semibaccata and Bassia hyssopifolia had successful germination at a wider range of soil conditions. The pattern of lower germination with low moisture levels was less pronounced for these species, and successful germination occurred at soil salinity levels of 20ppt and 30ppt, respectively. This indicates that non-native plants in the salt marsh vary in the extent to which germination is constrained by seasonal change in soil conditions. These results suggest that the potential management technique of controlling non-native plants through salt addition might not be effective for all non-native species. Species with a greater tolerance for high soil salinity and low moisture conditions might become more successful in the future, as rising sea levels and increase in drought conditions associated with global climate change create conditions that favor these species.