Response of native and exotic saltmarsh species to sediment deposition addition

The native saltmarsh species Scirpus mariqueter (hereafter S. mariqueter) and the exotic species saltmarsh cordgrass (Spartina alterniflora Loisel., hereafter S. alterniflora), have been found commonly in regional saltmarsh ecosystems which received a large amount of sediment inputs from Yangtze River, eastern coasts of China. For the purpose of saltmarsh restoration and invasive species management, it is important to understand the response of vegetation species to various sediment inputs. This study investigated and compared the effects of sediment addition on S. mariqueter and S. alterniflora through laboratory experiment using vegetation samples collected from a natural saltmarsh with a high sedimentation rate (12 cm a^-1). Plant growth parameters over their growth period, including survival rate, height and biomass were measured against sediment addition gradient (0 cm, 3 cm, 6 cm, 9 cm, and 12 cm in thickness). The results showed that sediment addition significantly affected the growth of vegetation but this effect varied between two species. Compared with the control group, the growth of S. mariqueter was promoted with sediment addition of 3-6 cm, but it turned to inhibition when the sediment thickness exceeded 6 cm. The growth of S. alterniflora was increased with increasing sediment addition till 9-12 cm, but the survival rate of each group kept stable. Overall, against a gradient sediment addition, S. mariqueter was found to benefit from low to moderate sediment addition (3-6 cm) but higher addition showed inhabitation effects. S. alterniflora benefited from increasing sediment addition to a point. When facing high sediment inputs, S. alterniflora was found to be more adaptable than S. mariqueter. These results have important implications for further studies on saltmarsh restoration and interspecific competition against a high sediment input background.