Nitrogen deposition mitigates ozone-induced stress in Quercus aliena: Transcriptomic and metabolomic perspectives

Ozone (O₃) pollution poses an increasingly serious threat to forest ecosystems. To investigate the effects of O₃ exposure on Quercus aliena and elucidate its defense mechanisms, we exposed Q. aliena to O₃ and monitored its responses using physiological, transcriptomic, and metabolomic analyses. The results revealed that after 84 days of O₃ exposure, the malondialdehyde (MDA) and proline contents in Q. aliena leaves significantly increased, while catalase (CAT) activity and soluble sugar content significantly decreased. Notably, N addition markedly alleviated O₃-induced oxidative stress. Integrated transcriptomic and metabolomic analyses revealed that N addition under O₃ stress modulated metabolic pathways associated with flavonoid biosynthesis and amino acid metabolism. Specifically, O₃ and N treatment increased the levels of rhoifolin, afzelechin, apigenin, luteoloside, kaempferol, and trifolin, while reducing the levels of phloretin, butin, cyanidin, taxifolin, myricetin, 2'-hydroxydaidzein, laricitrin, quercetin, prunin, luteolin, eriodictyol, quercitrin, and dihydromyricetin. Additionally, the co-treatment elevated the concentrations of L-glutamine, arginine, and ornithine, along with the levels of enzymes closely related to their synthesis, such as glnA (Uni0006561, Uni0006562, Uni0077758, Uni0101990), GSH (Uni0086646, Uni0101788), GSS (Uni0037737), and GCLC (Uni0034253). This study elucidates the metabolic alterations in Q. aliena under combined O₃ and N treatments, highlighting changes in flavonoid biosynthesis and amino acid metabolism pathways. Using a multi-omics approach, we provide comprehensive insights into the responses of Q. aliena to O₃ stress and N addition, offering significant implications for the management and conservation of forest ecosystems under environmental stress.