3种沉水植物对夏季高温强光照环境的生理响应

为了研究外来沉水植物伊乐藻（Elodea nuttallii）和埃格草（Egeria densa）对夏季自然高温强光照环境的生理响应，选择同科本地种轮叶黑藻（Hydrilla verticillata）作对比，在2014年8月夏季自然环境下进行实验处理，分别在第0、3、6、9、12、15天测定各物种的叶绿素含量、最大光能转化效率（Fv/Fm）、丙二醛含量和脯氨酸含量，以分析其变化情况。结果显示，高温与强光照对3种沉水植物的生理特征都有显著影响，特别是对其光合作用影响显著，且长期高温强光照环境的影响更大。第1-3天，温度升高至31℃左右，伊乐藻的叶绿素含量和3种植物的Fv/Fm显著低于初始值（P<0.05）；第4-6天温度持续在32℃左右，3种植物的叶绿素含量和Fv/Fm显著低于初始值（P<0.05），且伊乐藻和埃格草的丙二醛含量显著高于初始值（P<0.05）；除了第3天埃格草的叶绿素含量外，整个实验期间伊乐藻和埃格草的叶绿素含量和Fv/Fm显著低于初始值（P<0.05），在第12天和第15天时轮叶黑藻的叶绿素含量与初始值无明显差异（P>0.05），第9天和第12天轮叶黑藻的Fv/Fm与初始值无明显差异（P>0.05），并且整个实验期间轮叶黑藻的丙二醛含量和脯氨酸含量与初始值均无明显差异（P>0.05），表明轮叶黑藻通过较快恢复光合作用并维持体内抗氧化系统的稳定，对夏季高温强光照环境展现出较好的适应能力。光合作用能力降低以及长期高温强光照条件下，丙二醛含量显著增加，使得外来种伊乐藻和埃格草不适合在高温强光照环境中生长，夏季高温与强光照环境将会抑制其入侵和扩散。外来种伊乐藻和埃格草对高温强光照的耐受力低于本地种轮叶黑藻。

Physiological Response of Three Submerged Macrophytes to the High Temperature and Light Intensity of Summer

Invasion by exotic species has become a global problem, adversely affecting the environment, economy and even human health in the areas invaded. Elodea nuttallii and Egeria densa, belonging to Hydrocharitaceae, are two exotic submerged macrophytes species in China that display a strong invasive tendency. It has been reported that E. nuttallii and E. densa are both adapted to low temperature and light intensity. Thus, we investigated the physiological response of three Hydrocharitaceae species to the high temperature and light intensity of summer, including the two exotic species (E. nuttallii and E. densa) and one native species (Hydrilla verticillata). The study was designed to explore the effects of high temperature and light intensity on the invasiveness of the two exotic macrophytes. In August 2014, all test plants were placed in the natural summer condition of high temperature and light intensity, which provided the experimental treatment. The physiological response was measured by determining photosynthetic (total chlorophyll content and the maximum quantum yield of PSII (Fv/Fm)) and antioxidant (malondialdehyde and proline content) parameters. The physiological traits were measured on day 0, 3, 6, 9, 12, 15 of the treatment. Results show that high temperature and light intensity significantly affected the physiology of all three species, especially photosynthesis. Furthermore, long term high temperature and light intensity increased the impact. From day 1 to day 3, when the temperature rose to 31oC, the total chlorophyll content of E. nuttallii and the Fv/Fm of the three macrophytes were significantly lower than their initial levels (P<0.05). From day 4 to day 6, the temperature remained at 32 oC and the total chlorophyll content and the Fv/Fm of the three macrophytes were significantly lower than initially (P<0.05). Moreover, the MDA content of E. nuttallii and E. densa was significantly higher than the initial level (P<0.05). During the entire experiment, the total chlorophyll content and the Fv/Fm of E. nuttallii and E. densa were significantly lower than the initial levels (P < 0.05), except the total chlorophyll of E. densa on day 3. There was no significant difference in the total chlorophyll content of H. verticillata on day 12 or 15 and no significant difference in the Fv/Fm of H. verticillata on day 9 or 12. The malondialdehyde and proline content of H. verticillata did not change significantly during the experiment, indicating that H. verticillata is well adapted to summer conditions. The lower rate of photosynthesis and higher accumulation of malondialdehyde in E. nuttallii and E. densa during long-lasting conditions of high temperature and light intensity indicate stress. Thus, the native species, H. verticillata, has better tolerance to the summer conditions than the two exotic species, E. nuttallii and E. densa.