Interactive Effects of Increased UV-B and Rainfall on the Growth and Physiology of Tibetan Barley on the Tibetan Plateau

UV-B radiation and rainfall have tended to increase over the past decades in the Tibetan Plateau. A controlled field experiment, which simulated a 5% and 10% increase in UV-B radiation and a 10% and 20% increase in rainfall, was conducted to address the effects of enhanced UV-B radiation and increased rainfall on the leaf water potential, gas exchange, growth and biomass allocation, and phenology of Tibetan barley (Hordeum vulgare var. trifurcatum). Enhanced UV-B radiation conferred significant effects on the net photosynthetic rate (Pn), transpiration (E), stomatal conductance (gs), water use efficiency (WUE), total biomass, and spike length; the increased rainfall only affected Pn, E, and gs. These findings indicated that enhanced UV-B radiation had a more profound impact on the physiological and growth traits than the increased rainfall. Significant interactions of enhanced UV-B radiation and increased rainfall were also observed on leaf water potential, Pn, E, gs, WUE, total biomass, spike length, and relative growth rate. The leaf water potential was significantly increased with enhanced UV-B under the condition of a 20% increase in rainfall, Pn and biomass accumulation were also increased with enhanced UV-B under the conditions of increased rainfall, and the phenological stages were also delayed under ambient rainfall, but, this phenomenon disappeared gradually with an increased rainfall. It was therefore inferred that increased rainfall was able to offset the adverse impacts of enhanced UV-B radiation.