| 摘要: |
| 极端洪水显著地影响水生植物的生存环境，其带来的连锁效应可能是导致沉水植物大规模衰退的原因之一。极端洪水导致的外源营养、水位升高是影响沉水植物生长和繁殖的重要因素，因此以湖泊代表性沉水植物黑藻（Hydrilla verticillata）为对象，通过模拟研究探讨极端洪水事件导致的水位波动（水位在短时间内升高）及营养脉冲（营养物质在短时间内增加）对沉水植物、附着藻类和水体理化性质的影响。设置4种水位及营养盐负荷情景：对照（水位保持75 cm）、水位由75 cm逐步上升到150 cm+氮（N）磷（P）输入、水位由75 cm急剧上升到150 cm+NP输入以及水位保持75 cm+NP输入，其中后3项处理总N、P输入量相同，90 d内同步监测了浮游植物、附着藻类以及水体N、P浓度的变化。结果表明，对照组中，黑藻雌株相较于雄株个体更大，而极端降水（水位急剧上升）处理下，雄株的相对生长速率（RGR）、根生物量和繁殖器官数均大于雌株，表现出明显的性别二态性。雌性个体对水位波动（水位急剧上升和逐步上升）和营养脉冲的响应比雄性个体响应更为敏感。水位急剧上升和逐步上升均抑制了黑藻根生物量积累、RGR和主枝数，但株高、地上生物量和繁殖生物量保持稳定，水位急剧上升同时抑制了附着藻类的生长。营养脉冲提高了上覆水N浓度，促进浮游植物和周丛藻类生长，对黑藻地上部分、根和繁殖生物量均有显著抑制作用。实验设置的水位范围内，水位升高对黑藻的地上部分生长及繁殖的影响不明显，而N、P输入增加及水位波动的联合作用抑制了其地上部分生物量及繁殖输出，因此营养脉冲增强了水位升高对黑藻的影响效应。由此可以认为，极端洪水事件引起的水位波动叠加营养脉冲的复合效应会对沉水植物产生明显的抑制作用，随着未来降水强度和频率增加，而会对水生态系统造成较大的冲击。 |
| 关键词: 浅水湖泊 沉水植物 水位波动 富营养化 气候变化 有性繁殖 |
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| 基金项目:国家自然科学基金项目（32460285, 31960248），南昌大学江西省财政科技专项“包干制”试点示范项目（ZBG20230418010） |
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| Effects of increased nutrient loading and water level caused by extreme flooding on Hydrilla verticillata, periphyton and water properties |
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Luo Dong, Huang wenqiang, Ding Mingming, Li Lei
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School of Life Sciences, Nanchang University
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| Abstract: |
| Extreme flooding significantly affects the habitat of aquatic plants. Its knock-on effects may be one of the reasons for a massive decline in submerged macrophytes. Increased nutrient loading and rising water level are major factors affecting the reproduction and growth of submerged macrophytes. Therefore, we used H. verticillata, a typical submerged macrophyte in the lake, as the target species. A simulation study was conducted to explore the effects of water-level fluctuations (an increase in water level within a short period of time) and nutrient pulses (an increase in nutrient concentration within a short period of time) caused by extreme flooding events on the submerged macrophyte biomass, growth and reproductive traits, water physicochemical properties and periphyton. Four water level and nutrient loading scenarios were set up, i.e., control (stable water level of 75 cm), gradual increase of water level from 75 cm to 150 cm + nitrogen (N) and phosphorus (P) inputs, sudden increase in water level from 75 cm to 150 cm + N and P inputs, and stable water level of 75 cm + N and P inputs. The latter three treatments had identical total N and P inputs. Phytoplankton, periphyton and N and P concentrations in the water column were monitored in a 90-d period. The results showed that the sizes of females were greater than those of males in the control, while the relative growth rate (RGR), root biomass and the reproductive organ number in males were higher than those in females in the extreme precipitation treatment (sudden change in water level). These findings demonstrated an evident sexual dimorphism in H. verticillata. Females responded more sensitively than males to water-level fluctuations (sudden and gradual water level change) and nutrient pulses. Both sudden and gradual increase in water level suppressed root biomass, RGR and the main branch number of plants, whereas plant height, aboveground and reproductive biomass remained unchanged. At the same time, a sudden rise in water level inhibited periphyton growth. Nutrient pulses increased the N concentration in the overlying water, promoted phytoplankton and periphyton growth, and significantly inhibited the biomass of shoots, roots and reproductive tissues. Within the designed range of water levels (75-150 cm), increased water level had no significant effect on the aboveground growth and reproduction of plants, while the combined effect of increased N and P inputs and water-level fluctuations had a negative effect on both aboveground biomass and reproductive output. Thus, the nutrient pulses aggravated the effect of water-level fluctuations on H. verticillata. In conclusion, the joint effect of water-level fluctuations superimposed on nutrient pulses caused by extreme flooding events will have a significant inhibitory effect on submerged macrophytes. With the increasing intensity and frequency of precipitation in the future, it will cause considerable impacts on aquatic ecosystems. |
| Key words: Shallow lake submerged macrophyte water-level fluctuations eutrophication climate change sexual reproduction |
