Effects of elevated UV-B radiation on ecosystem and soil respiration in a winter wheat farmland

Abstract

O 3 concentration in the stratosphere is decreasing, resulting in higher solar ultraviolet-B radiation (UV-B, 280–320 nm) to the Earth’s surface. Enhanced levels of UV-B radiation may, in turn, alter ecosystem processes such as respiration. In this study, daily changes of ecosystem and soil respiration rates under modulated 20% supplementation of UV-B and ambient UV-B conditions (CK) were investigated in the 2007–08 winter wheat ( Triticum aestivum L.) season in a farmland nearing Nanjing city, south-east China, in order to determine the effects of elevated UV-B radiation on these processes. A paired t-test indicated that the effects of elevated UV-B radiation on ecosystem respiration varied across different measuring periods. Significantly lower ecosystem respiration rates in the elevated UV-B plots were found at the later growth (anthesis and beginning grain filling) stages. Elevated UV-B radiation significantly reduced soil respiration rates during each development stages. As far as the whole measuring period is concerned, elevated UV-B radiation significantly ( p < 0.05) reduced both ecosystem respiration and soil respiration. The seasonal mean ecosystem respiration rates for the CK and UV-B treatments were 1144.1 and 1008.3 mg CO 2 m −2 h −1, respectively, and the seasonal mean soil respiration rates for the two treatments were 286.0 and 249.3 mg CO 2 m −2 h −1, respectively. Regression analysis showed that elevated UV-B radiation significantly reduced temperature sensitivity of ecosystem respiration, with the Q 10 decreasing from 1.73 in the CK plots to 1.63 in the elevated UV-B plots. The Q 10 of soil respiration was not significantly affected by enhanced UV-B radiation. The exponential response curve (ecosystem respiration VS temperature) might be constructed with less-damaged plants at the lower temperature and more-damaged plants at the higher temperature, which yielded a lower temperature sensitivity of ecosystem respiration in the UV-B treatment.