Intermittent Root-Zone Aeration Partially Alleviates Waterlogging-Induced Root Hypoxia and Improves Growth, Photosynthetic Performance, Oxidative Balance, and Leaf Functional Quality in Mulberry Seedlings

Waterlogging restricts root-zone oxygen availability and can impair seedling growth and leaf quality in mulberry. Root-zone aeration may reduce waterlogging injury, but its effects on root anaerobic metabolism, photosynthesis, oxidative stress, and leaf functional quality have not been well integrated. In this study, Morus alba L. ‘Longsang No. 1’ seedlings were subjected to four treatments: normal moisture without aeration (CK), normal moisture with intermittent root-zone aeration (RA), waterlogging without aeration (WL), and waterlogging with intermittent root-zone aeration (WL+RA). Waterlogging was maintained with a water layer 1–2 cm above the substrate surface, and root-zone aeration was supplied using an air pump and microporous aeration stones for 30 min every 4 h. Root-zone dissolved oxygen, growth traits, root activity, root fermentative indicators, root and leaf oxidative injury, gas exchange, chlorophyll fluorescence, antioxidant enzyme activities, and leaf quality-related traits were measured after 14 d of treatment. Waterlogging decreased root-zone dissolved oxygen from 6.62 to 1.69 mg L−1. It also reduced plant height, total leaf area, shoot and root dry weight, root activity, Pn, Fv/Fm, Y(II), and ETR. In contrast, WL increased ADH and PDC activities, lactate and ethanol contents, MDA, H2O2, electrolyte leakage, and NPQ. Leaf 1-DNJ, polysaccharides, total phenolics, total flavonoids, DPPH, ABTS, and FRAP were also reduced under WL. Intermittent aeration increased root-zone dissolved oxygen to 4.64 mg L−1 under waterlogging and partially alleviated many of these changes. WL+RA showed higher growth, root activity, photosynthetic performance, PSII photochemical efficiency, antioxidant enzyme activities, and leaf functional quality than WL. These results indicate that intermittent root-zone aeration was associated with better mulberry seedling performance under waterlogging, together with changes in root-zone oxygen status, fermentation metabolism, photosynthesis, oxidative balance, and leaf quality.