The stratospheric ozone layer formed a protective atmospheric filter to avoid biologically harmful solar ultraviolet (UV) radiation. Nitrous oxide is the dominant ozone- depleting substance in the 21st century. Thus, the elevated UV-B radiation on earth's surface induced by ozone depletion has been regarded as one of the important issues in the field of global change. Rice is one of the predominant staple foods in the world, which feeds over 50% of the worldwide population for about 80% of their food requirements. Rice fields have been regarded as major anthropogenic sources of global methane (CH₄) emission. Many researchers reported that elevated UV-B radiation induced damage to growth, physiological and ecological processes in rice, including morphological inhibition, photosynthetic depression, unstable anti-oxidation system, changes in endogenous hormone content, decreases in biomass and yield. These reports were mainly concerned with the ecological and physiological processes in aboveground part of rice plant (shoot). However, nothing is known about the dynamics of CH₄ emission in paddy field during rice growing period under elevated UV-B radiation. Rice is also one of the crop species to which transgenic biotechnology has been successfully applied for genetic improvements such as disease and/or insect resistance, herbicide, drought and/or salt tolerance. However, transgenic rice has not yet been officially approved for commercial production in the world, because it is uncertain whether the rice will have any possible impacts on environmental and food safety. Therefore, safety assessment on transgenic rice was conducted to investigate gene flow through pollen transfer, change in biodiversity, non-target effects and food safety, etc. However, little attention has been paid to the effect of transgenic rice on CH₄ emission in paddy soil. Hence, the objective of this study was to investigate the dynamics of CH₄ emission in herbicide resistant transgenic rice from a paddy field under elevated UV-B radiation.
Field experiment was conducted to investigate methane (CH₄) emission as affected by elevated UV-B radiation. The field experiment was designed with two UV-B radiation levels, i.e. ambient (A, control) and elevated (E, 14.4 kJ·m^-2·d^-1 , simulating 25% stratospheric ozone depletion), and performed at the Station of Agricultural Meteorology, Nanjing University of Information Science and Technology, Nanjing, China. Two rice cultivars were tested in this experiment, including herbicide resistant transgenic rice (japonica line B2) and its parent conventional rice (japonica cv Xiushui 63). The transgenic line of japonica rice B2 contained bar gene with herbicide Basta resistance. CH₄ emission was determined by the closed chamber method at 10-day interval during rice growing period in a loamy clay paddy soil. The results indicated that, elevated UV-B radiation had no effect on seasonal dynamics of CH₄ flux in paddy field. Compared with control, elevated UV-B radiation significantly increased CH₄ flux and total amount of CH₄ emission. The sub-total amount of CH₄ emission peaked at tillering stage, and then jointing to booting stages, accounting for 51.55%-61.01% and 20.00%-26.64% of the total amount of CH₄ emission, respectively. Regardless of UV-B radiation, CH₄ flux and total amount of CH₄ emission were lower in transgenic rice than parent rice. It is suggested that planting herbicide resistant transgenic rice will be helpful in alleviating CH₄ emission from paddy fields under elevated UV-B radiation.