Plants may survive salinity and alkalinity with differential metabolic responses. The aim of this study was to gain further insights into the differential response to salinity and alkalinity stress at the metabolic level. Two Kentucky bluegrass, ‘Midnight’ (tolerant) and ‘Voyager II’ (sensitive), were subjected to salinity (NaCl, 75 mM Na+, pH 5.41) and alkalinity (Na2CO3 and NaHCO3, 75 mM Na+, pH 9.5) in hydroponics. The leaf metabolite profile was determined using gas chromatography–mass spectrometry (GC-MS). Alkaline salts caused more severe damages than neutral salt as indicated by the vertical shoot growth rate (VSGR), turf quality, electrolyte leakage (EL) and lipid peroxidation (MDA content). Adaptation of plants to salinity was mainly associated with the accumulation of amino acids (proline, valine, glutamate, asparagine, glutamine, phenylalanine and lysine) and sugars (sucrose, trehalose). In contrast, the metabolic response to alkalinity stress was mostly associated with the accumulation of organic acids that are mainly sugar acids (gluconate, galactarate, glucarate) and those involved in the citric acid cycle (malate, citrate, isocitrate, succinate, maleiate, aconitate). The differential accumulation of the amino acids, organic acids, sugars and fatty acids may contribute to the differential adaptation strategies due to their roles in the stress response pathways such as osmotic adjustment, membrane stability, respiration for energy production, carbon/nitrogen assimilation, regulation of the intracellular pH and the pH outside roots.
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