Effects of Water-Deficit Stress on the Growth and Physiological Characteristics of <i>Chloranthus spicatus</i> Seedlings

<i>Chloranthus spicatus</i> is one of the main scented tea varieties cultivated mainly in the Huangshan region, and dried flowers of these plants are mainly used for imparting a characteristic aroma to the tea. However, climatic variations in Huangshan limit its cultivation, with water deficit (WD) being the main limiting factor. The present study evaluated the effects of different WD intensities on the growth and physiological parameters of C. spicatus seedlings to determine the optimal soil moisture content for their large-scale cultivation. The experimental design comprised a control group (95–100%) and three treatment groups, namely mild WD (75–80%), moderate WD (55–60%), and severe WD (35–40%). Each treatment lasted 45 days and was given to 10 potted <i>C. spicatus</i> seedlings, with 3 replicates. Measurements were conducted for the shoot length and diameter; biomass; photosynthesis parameter; activities of antioxidant enzymes, namely superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT); and soluble protein (SP) and malonylaldehyde (MDA) contents of the seedlings. The results indicated that mild and moderate WD positively affected <i>C. spicatus</i> seedlings in terms of shoot length, diameter, biomass, root/shoot ratio, photosynthesis rate, intercellular CO₂ concentration, water use efficiency, and carboxylation efficiency. Moreover, the growth and photosynthesis were increased in the mild and moderate WD seedlings but decreased in the severe WD seedlings. Mild and moderate WD also led to a significant decrease in the antioxidant enzyme activities and the MDA content of seedlings (<i>p</i> < 0.05), all of which exhibited higher levels in severe WD seedlings. These results indicated that severe water stress restricted the growth of seedlings, while mild and moderate stress proved beneficial. SP content of the seedlings increased under mild and moderate WD but decreased under severe WD. We infer that the strong hydrophilicity of SPs in the seedlings results in the accumulation of water in plant cells, thus conferring resistance to drought stress. In conclusion, reducing the soil moisture content by 55–80% in the Huangshan region may be a promising strategy for boosting its cultivation.