Responses in Nitrogen Mass and Nitrogen Metabolism of Wild Sugarcane (Saccharum spontaneum L.) UV-B Radiation Under Field Conditions

Field experiments were conducted to evaluate effects of enhanced UV-B radiation (280-315 nm) on intraspecific responses in nitrogen mass and nitrogen metabolism of six wild sugarcane (Saccharum spontaneum L.) clones. The clones were collected from original sites with different altitudes (4-1780 m above sea-level) and latitudes (18-38°N). The supplemental UV-B radiation was 5.00 kJ⋅m^-2, simulating a depletion of 20% stratospheric ozone. Out of the six tested wild sugarcane clones, available Nitrogen (N) contents in soil and N contents in leaves of four wild sugarcane clones decreased significantly. Leaf biomass and leaf N mass of six wild sugarcane clones significantly increased. UV-B radiation significantly decreased N contents and increased biomass and N mass in stems of six wild sugarcane clones. Contents of free amino acid of two wild sugarcane clones (92-11 and 92-36) significantly decreased, whilst that of clones 83-193 and II91-5 significantly increased. Total protein contents of three wild sugarcane clones significantly decreased, whilst that of clone 90-15 significantly increased. Nitrate reductase activities of two clones (92-11 and 90-15) significantly decreased, whilst that of four clones significantly increased. Glutamine synthetase activities of two clones (92-11 and 90-15) significantly increased, while that of clones 83-193 significantly decreased. UV-B radiation might change stem biomass, resulting in changes in N mass in stem and leaves. Results indicate that intraspecific responses in N mass and N metabolism of six wild sugarcane (S. spontaneum) clones differing in UV sensitivity to enhanced UV-B radiation exist under field conditions.