Impact of Melatonin on Antioxidant Enzymes and Soluble Metabolites in Salt–Alkali-Stressed Poplar (Populus spp.): A Comparative Study of Pretreatment and Post-Treatment Effects. - Nai, Jiefei; He, Wanpeng; Ma, Tieming; Han, Xidong; Luo, Zhenxing; Li, Xinyu; Sun, Jiatong; Zhao, Xiyang (Forests (19994907), 2026)