不同UV-B辐射时间对菹草表型可塑性的影响

Effect of UV-B Radiation Time on Morphological Plasticity of Potamogeton crispus

菹草（Potamogeton crispus）衰亡的原因一直是水体生态修复的研究热点。已有的研究认为,强光照是促进菹草衰亡的关键因素。分别将菹草幼苗置于150μW/cm2剂量的中波紫外线（UV-B,波长为275-320 nm）辐射下,设置4种UV-B辐射持续时间处理,其每日的持续辐射时间分别设定为0 h（对照处理）、2 h、4 h和6 h,对照处理下的菹草幼苗不接受UV-B辐射,仅接受长波紫外线（UV-A）辐射和光合有效辐射,监测各处理下菹草幼苗的生长、形态状况、石芽形成和萌发等指标。研究结果表明,每日6 h的UV-B辐射,能促进菹草分枝,且能促进菹草衰亡;2 h和4 h的UV-B辐射,对菹草的影响较小,随着UV-B辐射时间的延长,菹草植株的株高、节间距和单株鲜质量明显下降,每日2 h的UV-B辐射,能促进植株叶面积的增加;每日延长UV-B辐射时间,可以促进石芽的形成,但形成的石芽随着变态率的增加,其长度增加、宽度减小,石芽质量减轻,下一个生长季的萌发率降低,萌发出二苗的比率降低,萌发苗的各项生长指标随着辐射剂量增加而逐渐降低。因此,在春末、夏初,随着太阳辐射时间的增加,阳光中累计的UV-B辐射剂量增加,这可能是促进菹草大批衰亡的重要原因。

Potamogeton crispus is important submersed macrophyte in purifying water and maintaining healthy aquatic ecosystems such as shallow lakes. Some researchers have reported that intense light is the key factor in Potamogeton crispus decline. We carried out a series of experiments to find the effect of UV-B radiation in the strong light on Potamogeton crispus decline. In this study, the seeding plants of Potamogeton crispus were exposed to ultraviolet B-band（275-320 nm） radiation in 150 μW/cm2, and for 2 hours, 4 hours, 6 hours everyday, the cumulative effective daily doses of UV-B radiation were 10.8 k J/m2, 21.6 k J/m2, and 32.4 k J/m2 respectively, and the control group was exposed only to ultraviolet A-band（320-400 nm） radiation andphotosynthetically active radiation（PAR）. Plant growth, plant height, internode length, leaf area and fresh weight were measured; turion number, weight, morphology and the germination indexes were monitored. The results showed that UV-B radiation could promote Potamogeton crispus to branch when the exposure within 6 hours everyday, but accelerated plant decline; UV-B radiation had a little influence on Potamogeton crispus growth when the irradiation within 2-4 hours. The plant height declined persistently with increasing UV-B radiationtime, the internode length decreased by UV-B radiation, the leaf area reduced, and the average fresh weight per plant decreased gradually with increasing radiation time, but the UV-B radiation could increase the leaf area when the radiation within 2 hours everyday. UV-B radiation increased turion quantity with increasing the radiation time, but the metamorphosis ratio of turion increased. When the exposure time of UV-B radiation increased, the turion length increased, whereas the turion width and weight reduced, the germination rate reduced in the next growing season. The germination rate and the ratio of two seedlings that germinated from these turions decreased and the seedling growth indexes（plant height, leaf number, leaf length, leaf width,leaf area, and so on） decreased significantly. The results indicated that cumulative UV-B radiation dose increased in late spring and early summer might be an important factor leading to mass mortality of Potamogeton crispus.