Comparison of the geographic variation in seed traits of a native species (Phragmites australis) to an alien invasive species (Spartina alterniflora) in Chinese coastal marshes

Abstract Seeds are crucial for both maintaining existing plant populations and for colonizing new areas, and knowledge of traits helps us understand the colonization potential of successful species. One way to study seed-trait variation is to make comparisons along latitudinal gradients. Usually, however, only geographic variation in seed mass is studied systematically and knowledge of other traits is lacking, e.g. traits associated with seed production and nutritional status. Moreover, there have been few comparisons between native species and exotic invasives. Here, therefore, we compared morphological traits and nutrient concentrations of the seed of two competing species, a native species (Phragmites australis) and an alien one (Spartina alterniflora) along a 20o-latitudinal gradient of the Chinese coast and investigated which environmental factors were important in driving differences between these two contrasting species. Significant differences were found between the two species for nine of the 13 traits in their responses to latitude. Furthermore, temperature-mediated climate factors were the dominant variables influencing the latitudinal variation of seed traits in both species compared to soil properties. For the first time, our study shows the latitudinal variations in seed traits of the native P. australis and alien S. alterniflora. Our study predicts that the greater fecundity of high-latitude S. alterniflora populations poses a threat to P. australis, the native competitor.