The Combined Effect Of Enhanced UV-B Radiation And Enriched CO₂ On The Fruit Quality And Yield Of Cucumber In Winter Plastic Greenhouse

The effects of enhancement of solar ultraviolet-B (UV-B, 280-320nm) radiation caused by ozone depletion and increasing atmospheric CO2 concentration resulting from environment damage on biosphere have already got comprehensive attention among the government and scientists. Plants growing in enhanced UV-B radiation or elevated CO2 concentration may change with their physiological, morphological structure and the process of growth and development directly or indirectly. Although there were extensive studies about biological and ecological effects o f single factor of them, little was known about the combined effect of enhanced UV-B and high CO2. In this paper, influence of enhanced UV-B and double CO2 concentration on the growth and development and quality and yield of cucumber were investigated in plastic greenhouse. The doses of UV-B were 0.581 kJ · m-2 ·d-1, 1.163 kJ · m-2·d-1, 1.744 kJ·m-2·d-1 and 2.905 kJ·m-2·d-1, and combined them with 700 μmol·mol-1 CO2 concentration. The results showed:(1) Under the condition of combined UV-B radiation with double CO2 concentration, the cucumber growed well, growth and development were accelerated Compared with the control, the results showed that the plant height, the petiole length, the leaf area and the diameter of stem were increased significantly by the combined treatment.(2) Photosynthesis rate was suppressed by the enhanced UV-B radiation, while promoted by the elevated CO2 concentration. Compared with contrast, the photosynthesis rate did not change much under the combined treatment. Stomatal conductance declined under UV-B radiation and elevated CO2 concentration respectively, while waiter use efficiency was increased by the combined treatment.(3) MDA content of cucumber leaf was increased by the UV-B radiation indicating the damage of cell membrane. UV-B absorbing compound content was increased too, which could prevent from the damage of UV-B radiation on plant cell.(4) In addition, the B2C treatment leaded to an increase in content of leaf chlorophyll and highest enzyme activity of SOD, POD and CAT. Soluble protein did not change apparently in all treatments.(5) In the aspect of quality and yield, the B2C treatment leaded to an increase in content of cucumber chlorophyll, fruit water, soluble protein, soluble sugar and Vc, and hence improved the quality of cucumbeis.(6) Except improving the content of soluble sugar, other indexes of B4C treatment were very closely to contrast. The reason is very likely that the effect of CO2 counteracted the injury of UV-B radiation.(7) The yield of cucumber was improved by the combined treatment, indicating that suitable dose UV-B combined with CO2 could improve the growth of cucumber, and increase the quality and yield, and that the combined effects were more significant than treatment of CO2 supplementary only.