Ultraviolet-B Radiation and Ozone Effects on Growth, Yield, and Photosynthesis of Soybean

The projected increase in solar ultraviolet-B (UV-B) radiation due to depletion of stratospheric ozone (O₃) has caused concern regarding possible UV-B damage to crops. At the same time, tropospheric O₃ is projected to remain at concentrations that are known to damage crops. Since these two stressors may co-occur, experiments were performed to determine their separate and joint effects on crop growth, yield, and photosynthesis. Open-top chambers, equipped with filtered UV-B lamp systems, were used in 3 yr of field studies to treat soybean [Glycine max (L.) Merr.; ‘Coker 6955’, ‘Essex’, and ‘S 53-34’] with supplemental UV-B radiation and/or O₃ from emergence through physiological maturity. Treatment levels of biologically effective UV-B radiation (UV-BBE) simulated the increase in ground level UV-B for stratospheric O₃ depletion up to 37% (approximately a doubling of ambient UV-BBE). Ozone treatment concentrations ranged from 14 to 83 nL L⁻¹ (seasonal mean 12 h d⁻¹ concentrations). Ultraviolet-B radiation did not affect soybean seed yield in any of the 3 yr of the study. In 1 yr, UV-B affected pod and seed number and pod weight, but the treatment means were not consistently related to the UV-B dose. No O₃ × UV-B interactions were found for any yield component at final harvest. Biweekly harvests of Essex during the growing season did not reveal any persistent effects of increased UV-B radiation on growth. Net carbon exchange rate (NCER), stomatal conductance, and transpiration of Essex soybean leaves were not suppressed by supplemental UV-B radiation. On the other hand, O₃ treatment consistently induced visible injury, suppressed NCER and water use efficiency, accelerated reproductive development, and suppressed growth and yield. It is concluded that tropospheric O₃ poses a greater threat to soybean production than projected levels of UV-B radiation. Cooperative investigations of the USDA-ARS and the North Carolina State University. The research reported in this publication was funded in part by the North Carolina Agric. Res. Serv. The use of trade names in this publication does not imply endorsement by the North Carolina Agric. Res. Serv. or the USDA of the products named, nor criticism of similar ones not mentioned.