Flooding effect on the distribution of native austral cordgrass Spartina densiflora in Patagonian Salt marshes

Abstract

Plant zonation is one of the most conspicuous ecological features of salt marshes worldwide. In Patagonian salt marshes the cordgrass Spartina alterniflora forms dense monospecific stands along the lowest marsh level, while the higher levels are dominated by Spartina densiflora or Sarcocornia perennis. In this study, we coupled field transplants combined with neighbor exclusion treatments and greenhouse experiments to evaluate the effect of submersion and waterlogged anoxic soil in the determination of the lower distribution limit of S. densiflora in Central Patagonian salt marshes within its native range. In the field experiment, no S. densiflora survived the frequent tidal submersion by approximately 2 m of seawater in the low marsh, independent of the S. alterniflora neighbors presence, while in the greenhouse experiment, all plants were able to tolerate strongly reducing soil conditions. Our results suggest that the absence of S. densiflora in the low marsh level is a consequence of the effect of the submersion, independent of the presence of S. alterniflora neighbors and of the strong soil anoxia. Our results contribute to optimize the efforts addressed to control or eradicate this exotic species in salt marshes where it is invading.