Differential nutrient uptake by saltmarsh plants is modified by increasing salinity

Abstract

In Southern European estuaries and associated saltmarshes, the anthropogenic nutrient inputs, together with longer drought periods, are leading to increasing eutrophication and salinization of these coastal ecosystems.In this study, uptake kinetics of NH4+, NO3-, and PO43- by 3 common plants in Palmones saltmarsh (Southern Spain), Sarcocornia perennis ssp. alpini, Atriplex portulacoides and Arthrocnemum macrostachyum were measured in hydroponic cultures.We also determined how these uptakes could be modified by increasing salinity, adding NaCl to the incubation medium (from 170 to 1,025mM).Kinetic parameters are analyzed to understand the competition of the three species for nutrient resources under realistic most frequent concentrations in the salt marsh.These results may also be useful to predict the possible changes in the community composition and distribution if trends in environmental changes persist. A. portulacoides showed the highest Vmax for NH4+, the most abundant nutrient in the salt marsh, while the highest affinity for this nutrient was observed in A. macrostachyum. Maximum uptake rates for NO3- were much lower than for NH4+, without significant differences among species.The highest Vmax value for PO43- was observed in A. macrostachyum, whereas A. portulacoides presented the highest affinity for this nutrient.High salinity drastically affected the physiological response of these species, decreasing nutrient uptake. S. perennis ssp. alpini and A. macrostachyum were not affected by salinity up to 510 mM NaCl, whereas A. portulacoides notably decreased its uptake capacity at 427mM and even withered at 1,025 mM NaCl. At current most frequent concentrations of NH4+ and PO43- in the salt marsh, S. perennis ssp. alpini is the most favored species, from the nutritional point of view. However, A.portulacoides could enhance its presence if the increasing NH4+ load continues, although a simultaneous salinization would negatively affect its nutritional physiology