Ecophysiological adaptations of two halophytes to salt stress: photosynthesis, PS II photochemistry and anti-oxidant feedback--implications for resilience in climate change.

Halimione portulacoides and Sarcocornia fruticosa commonly exhibit a reddish coloration especially in high evaporation periods, due to betacyanin production in response to stress. Although sharing the same area in salt marshes, they present different strategies to overcome salinity stress. While S. fruticosa present a dilution strategy, increasing succulence, H. portulacoides appears to have developed an ionic compartmentalization strategy. Nevertheless, there's still a decrease in the photosynthetic activity in different extents. While in S. fruticosa, the impairment of photosynthetic activity is due to a decrease in the flow from the electron transport chain to the quinone pool; in H. portulacoides the process is affected far more early, with high amounts of energy dissipated at the PSII light harvesting centers. This photosynthetic impairment leads to energy accumulation and consequently to the production of reactive oxygen species (ROS). SOD was particularly active in stressed individuals, although this increment is rather more significant in S. fruticosa than in H. portulacoides suggesting that H. portulacoides may have a maximum salt concentration at which can sustain cellular balance between ROS production and scavenging. These different ecophysiological responses have great importance while evaluating the impacts climate change driven increase of sediment salinity on halophyte physiology and on the marsh community and ecosystem services.