UVB acclimation promotes photosynthetic capacity without inhibition of biomass accumulation in cucumber

• UVB acclimation at the dose of 3 and 5 μmol m -2 s -1 promotes photosynthesis. • UVB acclimation increases the content of UV-absorbing compounds. • UVB acclimation enhances antioxidant capacity as affected by genotype. • UVB radiation (below 3 μmol m -2 s -1 ) does not reduce biomass accumulation. Cucumbers are distributed worldwide and are therefore exposed to varying levels of UVB radiation. However, the dose-response of cucumber to UVB radiation is unclear. Here, we examined the effects of different doses on photosynthetic performance, UV-absorbing compounds, antioxidant capacity, and growth in cucumber ( Cucumis sativus L.). Three originated cultivars (Changchunmici, Hexin9, and Hexin66) were exposed to UVB radiation at the intensity of 0, 3, and 5 μmol m -2 s -1 for 13 days. Results showed that UVB acclimation led to significant increase in light-saturated photosynthetic rate ( A sat ), with a more pronounced effect in Changchunmici than Hexin9 and Hexin66. The increase in A sat was supported by greater chlorophyll concentration on a leaf basis and thicker leaf, as well as higher antioxidant capacity. Meanwhile, UVB acclimation promoted the accumulation of UV-absorbing compounds (e.g., phenolics, flavonoids, flavonol) irrespective of cultivars, contributing to an enhanced screening or/and defense capacity to cope with UVB radiation. UVB acclimation at any level did not cause the adverse effect on growth parameters (e.g. shoot dry weight, leaf area, and leaf mass area) in all cultivars, except Changchunmici under 5 μmol m -2 s -1 UVB. Thus, we conclude that UVB acclimation within a suitable radiation range does not inhibit cucumber growth, instead, promotes photosynthetic capacity. The study would provide extensive understanding of horticultural plant responses to UVB radiation, facilitating light environment optimization in protected horticulture.