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Purely symbiotic and NO 3 -fed nodulated seedlings of  Virgilia oroboides  (Bergius) T.M. Salter,  Cyclopia maculata  (L.) Vent and  Podalyria calyptrata  Willd. were exposed to biologically effective ultraviolet-B radiation (UV-B) to assess the effects of above- and below-ambient UV-B on growth, symbiotic function and metabolite concentrations. Seedlings were grown outdoors either on tables under ambient or 34 or 66% above-ambient UV-B conditions (UV-B 100  control, UV-B 134  and UV-B 166 , respectively), or in chambers providing below-ambient (22% of ambient) UV-B (UV-B 22 ) along with a UV-A control and a photosynthetically active radiation (PAR) control. Exposure of seedlings to UV-B 166  radiation reduced ( P  ≤ 0.05) leaf and stem dry mass by 34 and 39%, respectively, in  C. maculata , and reduced leaf nitrogen concentration (%N) by 12% in  V. oroboides . Nodule %N in  C. maculata  and stem %N in  P. calyptrata  also decreased ( P  ≤ 0.05) in response to UV-B 22  radiation compared with the UV-A control, but not compared with the PAR control. Concentrations of flavonoids, soluble sugars and starch were unaltered by the UV-B treatments. Application of 1 mM NO 3  to UV-B 166 -treated seedlings increased whole-plant dry mass of  V. oroboides  and  P. calyptrata  by 47 and 52%, respectively. Dry mass of organs, nodule %N and total N concentration of these species also increased with NO 3  application. However, NO 3  supply decreased ( P  ≤ 0.05) nodule dry mass, stem %N and leaf %N as well as root and leaf anthocyanin concentrations in  C. maculata . In terms of UV-B × N interactions, dry mass of stems, roots, nodules and total biomass of NO 3 -fed  C. maculata  seedlings were reduced, and nodule %N, total N and leaf anthocyanins were depressed by the UV-B 134  and UV-B 166  treatments relative to UV-B 100 -treated seedlings. Although we found that above-ambient UV-B had no effects on growth and symbiotic function of  V. oroboides  and  P. calyptrata  seedlings, feeding NO 3  to these species increased ( P  ≤ 0.05) seedling growth. In contrast, purely symbiotic  C. maculata  seedlings were sensitive to the UV-B 166  radiation treatment, and adding NO 3  further increased their sensitivity to both the UV-B 134  and UV-B 166  treatments.

Responses to ultraviolet-B radiation by purely symbiotic and NO 3 -fed nodulated tree and shrub legumes indigenous to southern Africa