Elevated temperature has more pronounced effect on anthesis tomato plant than cadmium stress and reduced nitrogen supply

Plants are often exposed to combined stress, e.g. heat and cadmium (Cd) stress under natural conditions. Nitrogen (N) fertilizer is usually applied in excess, even though it is an essential nutrition for plants. We aimed to clarify the effects of elevated temperature, Cd stress, reduced N fertilizer and their interaction on leaf physiology and metabolism of anthesis tomato plants. Tomato plants at anthesis stage were subjected to unique combinations of elevated temperature (34 °C/30 °C), Cd stress (0.1 mM CdCl₂) and half N (N = 95 ppm) treatment. The elevated temperature generally decreased leaf intracellular CO₂ concentration and stomatal conductance, but increased transpiration rate with no significant changes in net photosynthetic rate, as compared with control. The plants under elevated temperature exhibited higher chlorophyll content as well as lower anthocyanin than under control temperature. The temperature had significant impacts on open flowers in the 1st inflorescence counting from bottom, open flower percentage in the 1st inflorescence, fresh and dry weight of flowers. Temperature played a predominant role in the changes of metabolites among the three factors based on metabolome. The Cd stress and reduced N supply also affected leaf metabolites of tomato plants, even though the effects on metabolites and physiology were less than that of elevated temperature. Trend analysis of the metabolites showed eight types in tomatoes under eight treatments. Biosynthesis of secondary metabolites, phenylpropanoid biosynthesis, linoleic acid metabolism and ABC transporters pathways positively responded to the elevated temperature. Moreover, there were significant interactions between the three factors (temperature, CdCl₂ and N) on tomato physiological and morphological parameters. We concluded that the physiological and metabolic responses of tomato plants were more pronounced to the elevated temperatures as compared with cadmium stress and reduced nitrogen fertilizer. This study can support the understanding of complex regulatory mechanisms in plants responding to multiple environmental changes due to climate change, management practice and environmental pollution.