Effects of enhanced UV-B radiation on morphology, physiology, biomass, leaf anatomy and ultrastructure in male and female mulberry (Morus alba) saplings

• Sexual differences in plant growth could be caused by enhanced UV-B radiation.
• Females suffer more severe damage on leaf development and photosynthetic capacity.
• More biomass is allocated to leaves in females but to roots and stems in males.
• Males possess a greater ability to relieve damage caused by UV-B radiation.

Effects of UV-B radiation on growth have been reported in many plants, but little attention has been paid to dioecious plants. To further address sexual differences in morphology, physiology, biomass, and leaf anatomy and ultrastructure could be induced by higher UV-B radiation, mulberry (Morus alba L.) saplings were chosen and subjected to ambient UV-B radiation (control) and enhanced UV-B radiation (10% higher than control) for one season’s growth. Compared with control, enhanced UV-B radiation damaged lamina epidermis and spongy parenchyma, injured chloroplast ultrastructure, significantly decreased shoot height (SH), basal diameter (BD), total leaf area (LA), specific leaf area, net photosynthetic rate (Pn), total dry mass (TM), relative chlorophyll content (SPAD) and carbon isotope composition (δ13C), and increased the ratio of aboveground/belowground mass (AB) and UV-B absorbing compounds in both male and female saplings. Moreover, under enhanced UV-B radiation, males received less injuries in leaf structure and chloroplasts, and had significant higher SH, BD, LA, TM, Pn, SPAD, δ13C, anthocyanin concentration but lower UV-B absorbing compounds and AB than female saplings. However, no significant sexual differences in these traits were observed under ambient UV-B radiation. Our results demonstrated that female plants would suffer more negative effects on morphology, physiology, biomass allocation and leaf structure than do males under enhanced UV-B radiation due to more resource requirement for reproductive development.