Metabolomics analysis reveals that elevated atmospheric CO2 alleviates drought stress in cucumber seedling leaves

Abstract Elevated atmospheric CO 2 alleviates moderate to severe drought stresses at physiological level in cucumber. To investigate the underlying metabolic mechanisms, cucumber seedlings were treated with two [CO 2 ] and three water treatments combinations, and their leaves were analyzed using a non-targeted metabolomics approach. The results showed that elevated [CO 2 ] changed 79 differential metabolites which were mainly associated with alanine, aspartate and glutamate metabolism; arginine and proline metabolism; TCA cycle; and glycerophospholipid metabolism under moderate drought stress. Moreover, elevated [CO 2 ] promoted the accumulation of secondary metabolites; including isoferulic acid, m-coumaric acid and salicyluric acid. Under severe drought stress, elevated [CO 2 ] changed 26 differential metabolites which mainly involved in alanine, aspartate and glutamate metabolism; pyruvate metabolism; arginine and proline metabolism; glyoxylate and dicarboxylate metabolism; cysteine and methionine metabolism; starch and sucrose metabolism; glycolysis or gluconeogenesis; and pyrimidine metabolism. In addition, elevated [CO 2 ] accumulated carbohydrates, 1,2,3-trihydroxybenzene, pyrocatechol, glutamate, and l -gulonolactone, to allow adaption to severe drought. In conclusion, the metabolites and metabolic pathways associated with the alleviation of drought stresses by elevated [CO 2 ] were different according to the level of drought stress. Our results may provide a theoretical basis for CO 2 fertilization and application of exogenous metabolites to enhance drought tolerance of cucumber.