Geographical variation on salt marshes plant species dominance and zonation along the Chilean Coast

Background/Question/Methods

The vertical zonation and dominance of salt marshes halophytic plants has long attracted the attention of ecologist, since their waterlogged soils can be anoxic and highly saline, limiting plants that do not have mechanisms to deal with the osmotic stress. On a geographical perspective, on the northern hemisphere, salt marsh plants may interact positively by ameliorating harsh physical conditions and positive interactions should be increasingly important at low latitudes, but also salt-sensitive species dominate most northern marshes whereas salt-tolerant species dominate most of the southern marshes. The Chilean coast is supported by narrow oceanic platform that reduce the occurrence of salt marshes just to the mouth of the rivers. Due to the lack of precipitations in most of the northern coast, river mouths are closed most part of the year, creating hyper saline conditions, whereas towards the south, the increase in precipitations reduce the saline load of the soil. The objective of our study was to describe salt marshes plant species composition, dominance and their zonation patterns along 2000 km of the Chilean coast and their relation with soil characteristics. We analyzed the plant species occurring on 18 saltmarshes along the coast. In each marsh, we surveyed plants cover by the use of 10, 1 x 1 m quadrats disposed over 5 transects running perpendicular to the coastline. Along each transect we also take soil samples to analyze their water content, salinity, and anoxic conditions.

Results/Conclusions

From 25°S to 28°S low intertidal zones are hyper saline and dominated by Distichlis spicata and by Sarcocornia fruticosa. Below 28°S following the rainfall increase and the decrease on soil salinity, Spartina densiflora cover increases whereas Sarcocornia fruticosa decreases, showing at both zones a clear pattern of vertical zonation. Then, south of 35°S, where mean precipitations are over 600 mm/year and the soil salinity is low, Spartina densiflora dominates the whole marsh and the vertical zonation disappeared. In these terms, the latitudinal variation on plants species dominance and their zonation on Chilean salt marshes are related not solely with the changes on precipitation but also with the reduction on soil salinity. Also, the changes on the vertical zonation pattern could be related with biological characteristics of the component species due to the fact that Spartina densiflora and Sarcocornia fruticosa are halophytes, but facultative the first and obligated the second.