Responses of Scirpus mariqueter and Spartina Alterniflora to simulated salt stress and salt-tolerance thresholds

As one of the key environmental factors, salinity affects survival, growth, and distribution of salt marsh plants. Given the projected sea level rise and saltwater intrusion, coastal wetland ecosystems are subject to higher salt stress, thus shifting in structure and function. Here, we focused on two vascular plants, a native species Scirpus mariqueter and an invasive species Spartina alterniflora in the Yangtze Estuary, aiming to explore the survival, growth, and reproduction of these two dominant species under a series of salinity stress. The responses of S. mariqueter and S. alterniflora to salinity were compared, and the salinity thresholds for survival of both species were calculated. The results showed that: (1) Survival rate of both species decreased as salinity increased, whereas the survival rate of S. alterniflora surpassed that of S. mariqueter under the same salinity (P<0.05). (2) Growth of both species was significantly curtailed by increasing salinity (P<0.05); plant height, aboveground and belowground biomass of S. mariqueter decreased as salinity increased, but those of S. alterniflora increased first then decreased when salinity reached >10‰ (3) Number of tillers and percent seed setting of both species decreased as salinity increased, suggesting an inhibited reproductive potential as affected by salinity; (4) S. mariqueter (with a salinity threshold of 21‰) was more susceptible to salinity than S. alterniflora (a salinity threshold of 43‰); (5) Being more salt-tolerant, the invasive S. alterni flora would overwhelm the native S. mariqueter under scenarios of sea level rise and saltwater intrusion.