Interpopulation Differences in Salinity Tolerance of the Invasive Cordgrass Spartina densiflora: Implications for Invasion Process

Abstract

The invasive cordgrass, Spartina densiflora, has demonstrated a high tolerance to salinity stress. However, no attempt has yet been made to assess the intra-specific variation in salinity tolerance among S. densiflora populations. The aim of this study was to analyze the effects of provenance and salinity (0, 80, 170, 510, and 1023 mM NaCl) on germination, seedling survival, growth, and physiological performance of S. densiflora adult plants from three populations of the Gulf of Cadiz (Odiel, Tinto, and Piedras, SW Spain). Our results indicate that a salinity increment decreased germination and seedling survival of all S. densiflora populations, but these impairments were also dependent on the original population of the seeds. Accordingly, the Odiel population showed greater germination (70 %) and seedling survival (86 %) percentages at 510 mM NaCl than Tinto and Piedras populations, with mean percentage values of 57 % germination and 55 % seedling survival. These differences were also clearly reflected in long-term measurements, such as those regarding total dry mass, relative growth rate, and tiller number, which were mainly determined by the extent of photosynthetic area rather than the variations in net photosynthetic rate. Also, the higher tolerance of the Odiel population could be partly explained by a reduced level of Na in its tissues. Consequently, all populations might have the ability to colonize brackish marshes and river banks, but their invasion would be severely limited under hypersaline conditions, except in the case of the Odiel population, which would have a greater capacity for invasion of sub-optimal habitats, such a salt pans.