Responses Of Celery Growth To Enhanced UV-B Radiation And Soil Water Stress

Vegetable production is an important part of agriculture. Nowdays high-quality vegetables production in plateau have shown good prospects. The vegetable bases in Gansu province is one of the five bigest vegetable bases in China for the high vegetables produced in the feasible natural conditions, which has become the bases of "vegetable output from western to eastern". The intensified surface UV-B (UV-B,280-315nm) radiation caused by the human activities has significantly effected the plateau plant growth and development. In the main growing areas for plateau summer vegetables, there are still no uniform standards for sound water management, the traditional irrigation methods such as furrow irrigation were still dominant irrigation methods, and there are no clear indicators to determine the irrigation starting point and irrigation amount. So it is very necessary to research the relation of water supply and demand of plateau summer vegetables for its good quality and high yield. Therefore it becomes extremely important to study the influencing pattern of the main meteorological factors on the celery integrated quality and seek counter measures for improving its quality. The celery physiological and biochemical adaptive response to enhanced UV-B radiation was researched under greenhouse condition, and the effects of light intensity and soil moisture on the celery growth, quality and photosynthetic characteristics were studied taking the variety "Ventura" as subject under field conditions in Yongchang County. The results are showed as follows:1. Intensified UV-B radiation experiment showed that Celery leaf photosynthetic pigment content decreased with the accumulation of radiation effects, chlorophyll a/b increased with the increasing of radiation intensity. The Pn, Gs, Tr, WUE values decreased with the increasing of radiation time and intensity. Pn and Gs were significantly positive correlated while irrelevant with the Ci. Celery could adapt to long-term mild UV-B radiation(0.2W/m2), but severe radiation (0.8W/m2) significantly reduced the net photosynthetic rate so that the "midday depression" time was extended to 3 hours. The impact of enhanced UV-B radiation on the photosynthesis of celery was caused by non-stomatal limitation factors. The POD and APX activity increased significantly and PAL activity decreased with increasing radiation intensity. MDA, soluble sugar, total phenol and flavonoid content increased with increasing radiation intensity and time. Enhanced UV-B radiation had no significant effect on the soluble protein content2. Light intensity experiment indicated that celery plant height, leaf number, biomass accumulation decreased with the reduced light intensity. Under 75 percent of the light intensity, Pn, Ls, Fv/Fm, ETR, cpPS (â…¡) values showed an increasing trend, while Fo, Fm increased at 50 percent of the light intensity. High light could increase the chlorophyll, carotenoids and cellulose content of celery stalk. Moderate shade favored the accumulation of vitamin C, soluble solids and semi-fiber. POD, SOD, CAT and APX activity were highest under 75% light intensity and decreased under 50% light intensity, but the enzyme activity of the two treatments were significantly higher than CK. MDA content was slightly higher under 75% light intensity compared to other treatments in the same stage, but the differences were not significant. Soluble sugar content showed increase-decrease-increase trend in the growth stage.3. Water stress experiment showed that the celery plant height, leaf number, biomass accumulation was significantly decreased under water stress. With the decreasing water supply and the increasing of water stress, SOD and CAT activity showed an increasing trend. APX activity significantly increased under severe stress. MDA content showed an linear increasing trend with the increasing of water stress. Celery soluble sugar content increased significantly under water stress comparing with CK, and differences between stress treatment and CK on soluble protein were not significant. Secondary metabolic substances of flavonoid and phenol content under treatments decreased slightly comparing with the control and the difference was not significant. The carotenoid content of stalk reduced significantly under severe water stress comparing with CK. The content of chlorophyll changed slightly and the differences between the treatments and CK were not significant. Vitamin C reduced and soluble solids content raised with the increasing of water stress. Within the dietary fiber in the celery stalk, half fiber content increased by 54.88% in severe stress conditions and 22.05% under mild stress than CK.Cellulose content also increased significantly, mild and severe stress treatment increased 36.64% and 50.32% respectively than CK. 4. Enhanced UV-B radiation and high light intensity significantly reduced celery photosynthetic productivity and affected its growth and quality formation. In the field production, light shading can be taken to reduce environmental stress to the celery crops and improve the quality. Celery is the vegetable crops with high water demand, reduced soil moisture inhibited its growth and caused significant reduction in production. The experimental study showed that the irrigation amount of 180-200m3/667m2 was suitable for celery growth.