Biochemical, photosynthetic and metabolomics insights of single and combined effects of salinity, heat, cold and drought in Arabidopsis.

Ensuring food security is one of the main challenges related to a growing global population under climate change conditions. The increasing soil salinity levels, drought, heatwaves, and late chilling severely threaten crops and often co-occur in field conditions. This work aims to provide deeper insight into the impact of single vs. combined abiotic stresses at the growth, biochemical and photosynthetic levels in Arabidopsis thaliana (L.). Reduced QY max was recorded in salinity-stressed plants, NPQ increased in heat and salinity single and combined stresses, and qP decreased in combined stresses. MDA and HO content were consistently altered under all stress conditions, but higher values were recorded under salinity alone and in combination. Salinity alone and in stress combinations (especially with cold) provided a stronger hierarchical effect. Despite glycine and GABA osmolytes not significantly changing, proline highlighted the hierarchically stronger impact of salinity, while glycine-betaine was decreased under drought combinations. Untargeted metabolomics pointed out distinct metabolic reprogramming triggered by the different stress conditions, alone or in combination. Pathway analysis revealed that abiotic stresses significantly affected hormones, amino acids and derivates, and secondary metabolites. Flavonoids accumulated under drought (alone and combined with heat and cold stresses), while N-containing compounds decreased under all combined stresses. Looking at the interactions across the parameters investigated, antagonistic, additive, or synergistic effects could be observed depending on the biochemical process considered. Notwithstanding, these results contribute to delving into the impact of various stress combinations, hierarchically highlighting the stress-specific effects and pointing out different combinations.