Differential Nutrient Uptake by Saltmarsh Plants Is Modified by Increasing Salinity.

Rocío Muñoz,Raquel Carmona,F Xavier Niell

doi:10.3389/fpls.2021.709453

Abstract

In Southern European estuaries and associated salt marshes, 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 ammonium, nitrate, and phosphate by three common plants in Palmones salt marsh (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 1,025 mM). 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. Atriplex portulacoides showed the highest Vmax for ammonium, the most abundant nutrient in the salt marsh, while the highest affinity for this nutrient was observed in A. macrostachyum. Maximum uptake rates for nitrate were much lower than for ammonium, without significant differences among species. The highest Vmax value for phosphate 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. Sarcocornia 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 427 mM and even withered at 1,025 mM NaCl. At current most frequent concentrations of ammonium and phosphate 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 ammonium load continues, although a simultaneous salinization would negatively affect its nutritional physiology.

Highlights

Salt marshes around the world are under threat, and understanding the responses to major environmental disturbances is critical to maintaining the health and conservation of these coastal ecosystems (Millennium Ecosystem Assessment, 2005; IPCC, 2014)
Our results reveal that Chenopodiacean plants studied have different uptake kinetic performances for ammonium, nitrate, and phosphate in hydroponic cultures, and that the effect of increasing salinity on them is species-specific
Kinetic parameters and nutrient uptake rates at real concentrations observed in the field may partly explain the local dominance of plant species

Summary

Introduction

Salt marshes around the world are under threat, and understanding the responses to major environmental disturbances is critical to maintaining the health and conservation of these coastal ecosystems (Millennium Ecosystem Assessment, 2005; IPCC, 2014). A concomitant salinization of coastal wetlands is occurring at an unprecedented rate and can be accelerated due to regional and global climate change (Herbert et al, 2015) This is the case of the salt marshes in Mediterranean climates, which are bearing more extreme events, as rising temperatures, floods, higher evaporation rates, and a decrease in rainfall and river flow (Ibañez et al, 1999; Álvarez-Rogel et al, 2000; Redondo-Gómez et al, 2007a; González-Alcaraz et al, 2014; Hassan et al, 2016; Cramer et al, 2018; Cañedo-Argüelles et al, 2019; Pereira et al, 2019; Vélez-Martín et al, 2020)

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