Effects Of Supplementary Ultraviolet-B Radiation On Plant Growth, Quality And Physiology Characteristics Of Non-Heading Chinese Cabbage

Problems such as low light transmission rate, especially low ultraviolet lighttransmission rate always existed in the coverage materials in protected cultivation. In lightsubstrate plug cultivation methods, the leaf vegetables grow so crowded that theirphotosynthetic areas are decreased. Furthermore, the problems also lead to overgrowth anduneven growth of the plant, which hamper quality of the vegetable. Ultraviolet radiationcan dwarf the plants; influence various aspects of the plants such as growth, development,photosynthesis, morphogenesis and biomass. Therefore, to supplement UV-B radiation fora short time span in the protected cultivation was expected to solve the above problems andimprove the growth and quality of leaf vegetables.Non-heading Chinese Cabbage cultivar 'Aijiao huang' was used as material to discussthe possibility of utilizing supplemental UV-B radiation to improve the growth and qualityof green house cultivated non-heading Chinese Cabbage, study the effects of supplementalUV-B radiation on growth, yield and quality, and fred some physiological and biochemicalchanges of the plants after supplemental UV-B radiation. Results were as follows;1. Plant growth, yield and quality were studied in Non-heading Chinese Cabbagegrown in green house condition irradiated with ultraviolet-B (UV-B) radiation for 7 daysin its initial period. UV-B irradiation intensity was 40, 50, 60μw·cm^-2 and irradiation timespan was 2h/d, 3h/d, 4h/d with ambient(CK). Results indicated that UV-B radiation hadinhibitory effects which increased with irradiation time span. On the 35th day, plantsirradiated with UV-B show no significant difference with CK in fresh mass, plant height,leaf number, dry matter content, chlorophyll content, soluble sugar, and nitrate content.However, plants irradiated with UV-B had higher Vc content and lower soluble protein thanCK, and the hypocotyls length was significantly lower, which illustrated that UV-Birradiation treatment had strong effect in control of the plant overgrowth. With all factorsconsidered, plants of the B₁ treatment combinations (UV-B radiation 40,50,60μw·cm^-2, time span 2h/d) are in effective control of overgrowth, enhanced of Vc content, while notdeclined in yield and quality.2. Effects of supplemental UV-B radiation in the initial period of the Non-headingChinese Cabbage plant in different light levels on the plant growth and physiologicalcharacteristics were studied. The indices of plants were tested in the 35th day. Aftersupplemental UV-B radiation in the initial period, fresh weight, dry weight, plant heightand PI of the plants in different treatments were significantly lower than those undernatural ultraviolet radiation in the same light density, and no significant difference of thoseindices were found among the supplemental UV-B radiation treatments. Under naturalultraviolet radiation condition of the greenhouse, fresh weight, dry weight, plant height andPI were declined with shading treatment. Vc content of the supplemental UV-B radiationtreatments was significantly higher than that of the natural ultraviolet radiation of thegreenhouse in different light density. SOD, POD, CAT activity and MDA content allchanged with the shading degree and after UV-B treatment, SOD, POD, CAT activity andMDA content were significantly increased.3. Effects of supplemental UV-B radiation in the initial period of the Non-headingChinese Cabbage plant in different light levels on the plant photosynthetic characteristicswere studied. Different light levels significantly influence the chlorophyll content of theplant leaves. In a same light level, no significant difference of Chl a, Chl b, totalChlorophyll and Chl a/b was found between the UV-B treatment and natural radiationtreatment. Net photosynthetic rate (Pn) and Transpiration (Tr) were decreased with theshading degree. Compared with the natural radiation and shading treatments, netphotosynthetic rate (Pn) of the UV-B radiated plants declined, intercellular CO₂concentration (Ci) and water use efficiency (WUE) increased, but there were no significantdifference in stomatal conductance (Gs) and transpiration (Tr). After UV-B radiationtreatment, Light Compensation Point (LCP) increased, Light saturation point (LSP),maximum net photosynthetic rate (P_max) and apparent quantum yield (AQY) decreased, butin different light density there were no consistent change rules.