Effect Of Enhanced UV-B And Different Nitrogen Level On Photosynthetic Characteristics Of Rice Leaves

Concentration of ozone in the stratosphere is increasingly reduce, it lead to a significant increase levels of solar UV-B radiation reaching the Earth’s surface. Plant physiological and biochemical metabolism to increased UV B radiation appeared a series of responses, more and more researchers have gotten the attention of this aspec.This experiment simulated UV-B radiation enhancement, with different nitrogen levels, studied whether the negative effect of UV-B radiation could be reduced by appropriate nitrogen. With the japonica rice variety Shennong 265 as materials, studied under the condition of pots. There are two kinds of light treatments:10% enhanced UV-B radiation (U) and natural light(U0), and three levels of nitrogen:low nitrogen(N1), middle nitrogen (N2) and high nitrogen (N3), a total of six treatments. Measured the light response characteristics, chlorophyll fluorescence characteristics, content of RuBP carboxylase, the changes of yield components of rice in tillering, jointing, flowering and filling, to discuss the effects of enhanced of UV-B radiation on the mechanism of photosynthetic physiological change and yields. The results are as follows:1. The impact on the photosynthetic characteristics(1)Under the same nitrogen level, enhanced UV-B radiation decreased the values of Pn、 Gs、Ls, but the Ci decreased at tillering and filling, the others stages no significant changes. Under the enhanced UV-B radiation level, with the increase of applying nitrogen, it will help to enhance photosynthesis, and the biggest increase in high nitrogen level. At the late of rice growth, middle nitrogen benefited to utilization of CO2, and improved photosynthetic rate. So in the early stages of rice stages, should guarantee the middle nitrogen level,therefore, the late stages with the high nitrogen can alleviate UV-Bradiation damage of rice leaves photosynthetic.(2)Change of these index responed was as follows:Under the same nitrogen level, the nigtive effects of UV-B radiation in tillering and fillering stages. The reason was that in the tillering stage, the rice plant was tender, the ability of photosynthetic was poor, and weaked against environmental stress, therefore, at late of rice growth, the negtive effect of UV-B radiation was decreased. Under the enhanced UV-B radiation level, with the increase of applying nitrogen, increased ability of photosynthetic.2. The effect on PS Ⅱ dynamic characteristics:(1) OJIP:point P decreased with radiation intensity increasing, reduced the fluorescence yield, and nitrogen fertilization could increase yield of fluorescence, the largest rise in middle nitrogen treatment. (2)The influence on PS Ⅱ center:Under the radiation treatment, Wk were higher, it OEC was damaged, and VJ, Sm, φo, N were decreased by radiation enhanced, especially decreased at the later stage of growth. But with the increase of nitrogen, it could relieve the damage in PS II center of UV-B radiation. (3) The effect of basic parameters of fluorescence:At the same nitrogen level, UV-B radiation reduced Fv/Fm, φPS Ⅱ, ETR, qP, NPQ. While, these values increased as the increasing dose of nitrogen. However, the high nitrogen treatment reduced NPQ at later growth stage.3. The effect on rubisco content:rubisco content of leaves was decreased in different stages with the enhanced UV-B radiation. Under different nitrogen level on rubisco content has a trend as UN3> UN2> UN1. Late rice growth as the increasing dose of nitrogen can made rubisco content increase, promote the photosynthesis.4. The effect on the yield and yield components:Enhanced UV-B radiation decreased yield and yield components, and the number of panicles per plant biggest declined. Effect of UV-B radiation under different nitrogen level on yield components showed:the number of panicles per plant had a trend as UN2>UN3>UNi, the panicle length, seed-setting rate and yield had a trend as UN3> UN2> UN1. The number of grains per panicle was maximum, under UN3 treatment, while UN1, UN2 difference was not significant. Primary branches and the grain weight were not significantly change under different treatments. Under UV-B radiation, number of panicles per plant, grains per panicle, and yield were increased as the increasing dose of nitrogen.