Abstract: We investigated the drought adaptation mechanisms associated with root morphological reshaping and antioxidant synergy in Cinnamomum camphora, to provide a theoretical foundation for optimizing the seedling nursery strategies and advancing water-saving forestry practices. We conducted a pot experiment with 6-month-old Cinnamomum camphora seedlings along a simulated drought stress gradient. There were four water treatments: CK (control, 80%-85% of field capacity), LD (light drought, 65%-70% of field capacity), MD (moderate drought, 50%-55% of field capacity), and SD (severe drought, 35%-40% of field capacity). The growth and physiological responses of seedlings were analyzed. The results showed that mild drought (LD) promoted seedling growth. Under LD, total biomass, root length, root surface area, and root volume increased by 51.15%, 29.09%, 57.18%, and 68.46%, respectively. In contrast, moderate (MD) and severe drought (SD) treatments exerted a significant inhibitory effect on seedling growth. The antioxidant system was modulated primarily through enhanced superoxide dismutase (SOD) activity. Specifically, under MD and SD treatments, SOD activity significantly increased by 75.72% and 76.85%, respectively (P<0.05). The SD treatment significantly elevated the contents of soluble protein, soluble sugar, and proline by 81.56%, 45.64%, and 34.06%, respectively (P<0.05). Analysis of phenotypic plasticity revealed that ground stem growth, peroxidase (POD) activity, SOD activity, and proline content exhibited the highest plasticity indices. Principal component analysis indicated that LD was more strongly associated with variations in chlorophyll a, chlorophyll b, and malondialdehyde (MDA) contents, whereas MD and SD were more closely linked to variations in SOD activity, soluble sugar, and proline contents. Under MD and SD conditions, C. camphora seedlings enhanced drought resistance through an integrated strategy, including reduced growth rate, root morphological reshaping, regulation of antioxidant enzyme synthesis (mainly SOD), and enhanced osmotic adjustment (primarily via proline accumulation). The beneficial effect of mild drought (LD) identified here provides key indicators for water-saving seedling cultivation, such as root morphological plasticity and SOD activity. A soil moisture level of 65%-70% of field capacity is recommended. These indicators are also valuable for screening drought-resistant C. camphora cultivars.

Key words: drought, root morphology, antioxidant system, drought gain effect