Climate-Dependent Effects of Root Restriction on Yield and Quality of Netted Melon in a South China Greenhouse

We investigated the effects of a root-restricted cultivation experiment of netted melons in a greenhouse in south China over two cropping seasons (autumn–winter and spring–summer) with three root-zone volumes (R1: 15 L/plant, R2: 5 L/plant, and R3: 0.75 L/plant) on fruit production and quality. Seasonal temperature and light conditions significantly regulate the balance between yield and quality of netted melons. The high-temperature and strong-light environment in summer promotes vigorous plant growth, fruit expansion and the formation of coarse reticulation, achieving high yield, but it leads to a significant reduction in the content of soluble solids, Vc, soluble protein and antioxidant substances. Under the low-temperature and weak-light conditions in autumn, plants increase the angle between stems and leaves to enhance light interception. Although the fruits are small and the reticulation is fine, they accumulate higher levels of sugar, nutrients and antioxidant substances due to the large diurnal temperature difference. Furthermore, the effect of root restriction cultivation is significantly climate-dependent: severe root restriction (R3) can increase the harvest index in both seasons and improve the fineness of the reticulation in autumn, but it inhibits growth. Therefore, root-zone volume is the key to regulating comprehensive performance, and strategies should be optimized in combination with the climate background: moderate (R2) root restriction in autumn is suitable for improving quality and yield, while severe root restriction (R3) in summer has potential applications in specific quality indicators.