| Emissions of ozone (O3) precursors of methane and NOx due to human activity and fossil-fuel combustion leaded to an increase in ground-level O3 in Yangtze River Delta, China, At present, the adverse effects of O3 on wheat have been reported extensively. Meanwhile The extensive research showed that UV-B radiation (UV-B:280-320 nm) is also a menace to many crops. The study on the influencing mechanism and influence degree of the compound stress on winter wheat is of profound theoretical and practical significance. In this study, with open-top chambers established in the field in Nanjing we investigated the responses of winter wheat to elevated UV-B and O3 levels at different growth stages, and analyzed yield components at harvest time. This study provides the first-hand field observations for studying the compound effects of two important environmental factors (UV-B and O3) that are projected to change in the future climate on winter wheat growth and development. The experimental design consisted of eight treatments:CK (the control, natural solar UV-B irradiance, ambient air with approximately 50nl·L-1O3), EU1(10% higher level of UV-B intensity, ambient air with approximately 50 nl·L-1 O3),EU2(20% higher level of UV-B intensity, ambient air with approximately 50 nl·L-1O3), EO1(natural solar UV-B irradiance, mixed gas with approximately 100 nl·L-1 O3), EO2(natural solar UV-B irradiance, mixed gas with approximately 150 nl·L-1O3),EU1+EO1(10% higher level of UV-B intensity, mixed gas with approximately 100 nl·L-1O3), EU2+EO1(20% higher level of UV-B intensity, mixed gas with approximately 100 nl-L-1O3), EUl+EO2(10% higher level of UV-B intensity, mixed gas with approximately 150 nl-L-1O3). The main conclusions of this paper were as follows:(1)From booting stage to blooming stage, the interactive stress of UV-B and O3 significantly decreased leaf area index, with the reductions larger than those under single stress, however, in filling and ripening stage, the leaf area index under compound stress was lager than that under single stress. From blooming to ripening and the compound effects of UV-B and O3 on leaf number per plant and leaf area per leaf can be explained as antagonistic action. There was no significant difference in the plant height and internode number. In filling and ripening the topmost knop length under compound stress was between those under EU and EO. The compound effects of UV-B and O3 can alleviate the adverse effects of O3 to stem diameter of winter wheat. Compared to the contral, the morpha response index under 20% higher level of UV-B intensity, mixed gas with approximately 100 nl·L-1 O3 and the compound stress is 49.4%,32.87%,33.25% respectively. The compound effects of UV-B and O3 on morphological character of winter wheat were not simple additive relation.(2) Under the interactive stress of ultraviolet-B and O3, the content of chlorophyll decreased very significantly, and the reductions had no significant difference with that under the single stress of UV-B. Malonaldehyde and flavonoids increased markedly with the increment larger than those under single stress after blooming. Dry matter weight decreased significantly with the decrements larger than that under any single stress in filling and ripening; The partitioning index of leaves was higher than that under other treatments in filling and ripening; The partitioning index of stalk decreased significantly with the decreament larger than that single stress; The partitioning index of grains was higher than that under ultraviolet-B treatment and lower than that under O3 treatment in later filling stage; However, no significant difference was detected in the partitioning index of stem. Under EU2 condition, the contribution of leaves was dcreased by 35.01%(P<0.01), however, under the EOl condition, the contribution of stalk wase increased by 7.63%(P<0.01). Under the compound stress, the average content of soluble sugar in the flag leaf and contribution of stem decreased significantly, which leaded to significant declines in both grains per panicle and 1000-grains weight. Compared to the contral, the yield of winter wheat under 20% higher level of UV-B intensity, mixed gas with approximately 100nl·L-1 O3 and the compound stress is reduced by 31.54%(P<0.05),23.64%(P<0.05),40.72%(P<0.01) respectinely. The above results showed that the filling-ripening stage is the sensitive developmental period of winter wheat under the compound stress.Different indicators for growth and physiology of winter wheat exhibited different compound effects in response to the interactive stresses of ultraviolet-B and O3.(3) A dynamic model is established in this study and runs under a Vensim PLE software. Indices (fc1, fc2) were built in the model to explore how the plant response to the stresses. Additionally, the correlation between the stress factors for UV-B intensity and O3 concentration and the increase rate of the fraction of grain weight was established to simulate the yield formation. The model was examined via experimental document. Results showed that the model has good performances on predicting the dynamic formation of total dry matter, aboveground dry matter and yield of winter wheat. The correlation coefficients between observed value and simulated value were significant (P<0.01). The relative errors (RE) for total dry matter, aboveground dry matter and grain weight were 9.05%,10.01%,16.19%, respectively. The model demonstrated that elevated UV-B and O3 has synergistic impacts on dry matter production, biological yield and yield formation in later filling stage of winter wheat. |
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