UV-B辐射胁迫对杨桐幼苗生长及光合生理的影响

通过对UV-B辐射胁迫下亚热带典型木本杨桐幼苗的生长及光合生理的研究,探讨植物对于UV-B辐射胁迫的生理响应及适应性机理,进而揭示UV-B辐射变化对亚热带森林树种的影响.实验设置UV-B辐射滤光组、自然光对照组以及辐射增强组,选择亚热带典型树种杨桐(Cleyera japonica Thunb.)幼苗为实验材料.研究结果表明:(1)增强UV-B辐射会降低杨桐幼苗的叶绿素含量,而降低辐射则会显著促进叶绿素的增加,且这种胁迫在时间上具有积累性.(2)增强或降低辐射强度都会抑制杨桐地径的生长,增强辐射会产生更显著的抑制；降低辐射强度会对杨桐幼苗的株高生长产生促进作用,反之,则会抑制其生长.3个测定期数据综合分析显示随着处理时间的加长,这种胁迫作用有减小的趋势.(3)对光响应曲线的分析表明相对于自然光条件下的UV-B辐射,降低其强度对杨桐幼苗光合作用有显著的促进作用,反之则会抑制,不过抑制作用并不显著；对于光合特征参数的分析表明增强或降低UV-B辐射会显著降低杨桐幼苗的光饱和点(LSP)和光补偿点(LcP),而对最大净光合速率(Amax)、表观光合量子效率(AQY)、暗呼吸速率(Rd)影响均不显著,表明辐射胁迫对杨桐幼苗利用光能的效率影响不大,从而也并未对杨桐的光合作用产生显著性的伤害,但是由于森林树种的多年生特性,这种影响将是积累性的或延迟的,UV-B所造成的光合作用或光能利用率的微小变化都可能会积累成长期影响.因此,对森林树种进行长期研究是必要的.

The growth and photosynthetic responses of Cleyera japonica Thunb. seedlings to UV-B radiation stress

In order to reveal the impact of the UV-B radiation on the woody plants in subtropical regions of China, the paper researches the effects of UV-B radiation stress on photosynthetic and physiological characters of typical woody plant Cleyera japonica Thunb. seedlings. Blocked UV-B group(BU),Solar UV group(CK) and enhanced UV-B group(EU) were set for field experiment in which C. japonica seedlings were selected as experimental material. Measurements were carried out from August 2007 to July 2009(base data was from August 2007).Results showed a great variety of UV-B effects on photosynthesis,morphology and growth, which are that:(1)The decreased UV-B radiation significantly increased the amount of the chlorophyll of C. japonica (P<0.05),while the enhanced UV-B radiation reduced the chlorophyll content. Furthermore, the parameter comparison of three growth seasons revealed that more and more significant reduction of the chlorophyll content occurred under enhanced UV-B radiation over time, which could be interpreted as a cumulative UV-B effect on the seedlings and would likely bring a negative effect on the photosynthesis of the seedlings in the long term treatment. (2) Plant height and main stem diameter were measured at the full bloom stage. Both the enhanced and decreased UV-B radiation could inhibited the stem diameter of C. japonica seedlings and the former inhibition proved to be more effective than the latter one. The height could be promoted under decreased UV-B radiation, inhibited under enhanced one. The different responses between plant height and stem diameter to UV-B radiation treatment suggests that not only the growth rate but also the internal growth mechanism of C. japonica seedlings was changing under the UV-B radiation stress. The parameter comparison of three growth seasons exhibited a tendency to decreased stress on the growth of C. japonica seedlings as the treat time went by. UV-B-absorbing compounds, which accumulate to shield plants against harmful UV-B radiation by absorbing UV-B radiation, were the best explanation and most effective self-protective responses of plants to UV-B radiation. (3)Significantly promoted photosynthesis was observed in C. japonica seedlings in response to decreased UV-B radiation according to the analysis of light response curves, while the inhibited effect was observed under enhanced UV-B radiation, the inhibition was not significant yet. Analysis of photosynthetic characteristic parameter demonstrated that both the enhanced and decreased UV-B radiation could induced significantly reduction in light saturation point(LSP) and light compensation point(LCP) during the 3-year study period, nevertheless, the scarcely significant changes of the maximum net photosynthetic rate(A_max),apparent quantum yield(AQY) and dark respiration rate(R_d) were observed, indicating that UV-B radiation exerted no significant influence on the light use efficiency of the seedlings. In brief, large increases in UV-B radiation were unlikely to have a significant negative effect on the photosynthesis of C. japonica seedlings in the short term. As UV-B effects may be cumulative or delayed, and woody plants are long-lived, the relatively small changes in photosynthesis or the light use efficiency which were observed in our study may result in some long-term effects. Therefore,the long-term and multiple-season field study on woody plants is necessary in the future.