Effect Of Elevated UV-B Radiation On Soil Biological Properties In Barley Cultivars

Elevated ultraviolet-B (UV-B) radiation induced by the depletion of stratospheric ozone layer has been regarded as one of the important problems in global change. More attentions have been paid to the effects of elevated UV-B radiation on ecological processes in agro-ecosystem. Pot and field simulating experiments were conducted to investigate the effects of elevated UV-B radiation on biological properties in three barley cultivars. The experiment was designed with two UV-B radiation levels, i.e. ambient (A, control,1.5kJ·m-2·h-1) and elevated by20%(E,1.8kJ·m-2·h-1). The tested barley cultivars included Dan2, Supi3and Supi4, which are widely cultivated and regarded as the typical cultivars in Jiangsu province, China. Soil and gas samples were collected at the main growth stages of barley, i.e. tillering stage, jointing, booting, heading and maturity, to determine microbial biomass carbon, some enzymatic activities and soil respiration rate in barley rhizosphere and non-rhizosphere soils. This study is helpful in assessing the transformation of soil organic C in barley under elevated UV-B radiation. The main results are listed as follows:(1) Elevated UV-B radiation obviously decreased the content of microbial biomass carbon in barley rhizosphere and non-rhizosphere soils, but the significances depending on growth stages in barley cultivars, but had no effect on the tendency of microbial biomass C during the entire barley growing season. At barley late growth stages (heading and maturity), the content of microbial biomass carbon under greenhouse conditions was lower than that under filed conditions.(2) Compared with the control, elevated UV-B radiation clearly reduced soil respiration rate and its temperature sensitivity coefficient Q10values, especially in in Supi3and Dan2(P <0.05), but increase in Q10value was observed in Supi4. Elevated UV-B radiation obviously promoted metabolic quotients in the rhizosphere and non-rhizosphere soils, but had no impacts on the trend of metabolic quotient during barley growth season.(3) Compared with the control, elevated UV-B radiation effects on soil enzymatic activities changed with barley cultivars. In Dan2cultivar, elevated UV-B radiation obviously increased the activities of dehydrogenase and invertase, but decreased amylase activity in barley rhizosphere soil; In Supi3cultivar, elevated UV-B radiation distinctly promoted the activities of dehydrogenase, amylase and invertase in barley rhizosphere soil; In Supi4cultivar, elevated UV-B radiation clearly reduced dehydrogenase activity, but increased the activities of amylase and invertase in barley rhizosphere soil.(4) Regardless of pot or field experiment, no significant differences were observed in the activities of dehydrogenase, amylase and invertase between the two levels of UV-B radiation (ambient and elevated) in barely rhizosphere or non-rhizosphere soil.(5) It is suggested that the different responses of three barley cultivars to elevated UV-B radiation were related to the changes of microbial biomass C and soil respiration.