ALTERATION IN THE MINERAL NUTRITION OF PURELY SYMBIOTIC AND NITRATE-FED NODULATED LEGUMES EXPOSED TO ELEVATED UV-B RADIATION

Abstract

The effects of elevated UV-B radiation and two nitrogen (N) sources on mineral nutrition of Cyclopia maculata, a UV-B-sensitive species, was assessed together with UV-B-tolerant symbiotic legumes Vigna unguiculata, Glycine max, Lupinus luteus, Vicia atropurpurea, Podalyria calyptrata and Virgilia oroboides. Plants were grown outdoors on tables under moderately or highly elevated UV-B exposures which simulated 15% and 25% ozone depletion above Cape Town in South Africa. Exposing purely symbiotic plants of V. unguiculata to elevated UV-B132 radiation decreased the tissue concentration of calcium (Ca) in leaves, phosphorus (P) in stems and roots, potassium (K) in roots, and boron (B) in roots and nodules relative to UV-B162 or ambient control. In contrast, seedlings of C. maculata, V. oroboides, L. luteus, and V. atropurpurea plants exposed to elevated UV-B radiation increased the concentration of several nutrients in leaves, stems and roots whereas P. calyptrata showed no changes in the mineral nutrition. The reported reduction in plant dry matter yield in C. maculata was accompanied with increased concentrations of P, K, Ca, magnesium (Mg), copper (Cu), and manganese (Mn) in photosynthetic leaves and stems, suggesting that the reported decrease in biomass yield could not be attributed to limitations associated with nutrient uptake. Our results suggest that factors other than limitations of nutrient uptake contributed to the reduced biomass accumulation of purely symbiotic and nitrate (NO3 −)-fed nodulated seedlings of C. maculata.