Soil chemical composition modifies the morpho-physiological responses of Prosopis strombulifera, a halophyte native to South America.

Abstract In some salty areas of South America, and especially in central Argentina, high levels of sodium sulfate (Na2SO4) are found together with sodium chloride (NaCl). Plant species show differences in their susceptibility to growth in the presence of these salts. Some studies showed that Na2SO4 may inhibit the growth of species such as wheat, sugarcane, beet, tomato, wild potato and barley more than NaCl. However, studies focusing on how sodium sulfate can affect the biochemical and physiological processes of plants are very scarce. This chapter provides an overview of the tolerance/non-tolerance mechanisms of the halophyte Prosopis strombulifera, with a special emphasis on the effects of Na2SO4 on growth parameters, ion accumulation, production of secondary metabolites, antioxidant system and hormonal regulation, showing that the presence of the SO42- anion in the culture medium was determinant in the toxicity observed in P. strombulifera plants treated with Na2SO4. It is proposed that, as SO42- assimilation may be limited by the high concentration in the culture medium, the sulfur that has not been metabolized to cysteine would be in excess; it may be binding to cytochrome b559 of PSII, blocking its activity partially or completely, and thus inhibiting photosynthesis. Carbon metabolism and partitioning of Na2SO4 treated plants are also affected, and energy resources should be diverted to synthesis of secondary metabolites such as condensed tannins and lignin, and polyphenol precursors, to cope with the high oxidative stress. As a consequence, there is a strong inhibition in the growth of Na2SO4 treated plants, leading to chlorosis, necrosis and foliar abscission.