| 摘要: |
| 据全球气候变化模型预测，未来极端洪水事件将呈现增多和加剧态势。极端洪水对沉水植物功能性状、生长发育状况及整个生态系统均有深远的影响，研究极端洪水对沉水植物生长发育的影响对理解和预测气候变化过程中水生态系统的变化具有重要意义。本文针对极端洪水事件引起的水位急剧上升和营养负荷量增加双重效应，在实验周期90 d内设置对照（水位保持75 cm）、2种极端洪水条件（水位在第1天从75 cm快速上升至150 cm + NP输入、水位从75 cm逐步上升至150 cm + NP输入）以及水位保持75 cm + NP输入4项处理（后3项处理中营养输入总量相同），研究了极端洪水对沉水植物苦草（Vallisneria natans）生长、繁殖对策及生物量分配的影响，实验过程中还同步监测了浮游植物、附着藻类和水体营养状况（TN和TP）。在苦草的17个测定指标中，只有根生物量分配和有性繁殖分配在4个处理下无明显变化。从水位的单独作用看，相对于营养增加且水位恒定的处理，两种洪水条件（水位急剧上升和逐步上升）均降低了苦草的分株数、叶片数、间隔子数、间隔子总长、最大根长、花果数以及各器官生物量和总生物量，促进了人工基质表面附着藻类的生长。水位急剧上升时，植株对间隔子的生物量投资倾向于最小，而株高和植株对叶的生物量投资倾向于最大。从营养负荷的单独作用来看，相对于对照组，营养增加且水位恒定的处理中水体N浓度显著增加，促进浮游植物和苦草表面附着藻类的生长，但是从二者Chl.a浓度来看，浮游植物遮光作用相对较大，抑制了苦草叶、根和间隔子的生长，但有性繁殖生物量无明显变化。从水位和营养负荷联合作用的模式来看，水位上升和营养负荷两个环境因素的联合作用会使入湖营养负荷加强水位上升对沉水植物生长的影响效应，二者的联合作用使叶、根、间隔子和有性繁殖生物量均大大降低。因此，极端洪水对沉水植物的不利影响较大，不仅由于水位抬升直接影响沉水植物，还会通过浮游植物间接影响沉水植物生长发育。 |
| 关键词: 沉水植物 苦草 水位 营养负荷 浮游植物 附着藻类 |
| DOI： |
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| 基金项目:国家自然科学基金项目 |
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| Combined influence of extreme flooding-induced water level increase and N and P inputs on the submerged macrophyte Vallisneria natans |
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Ding Mingming1, Li Lei1, Gong Leiqiang2, Zhan Huiying2
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1.Jiangxi Province Key Laboratory of Watershed Ecosystem Change and Biodiversity, Center for Watershed Ecology, Institute of Life Science and School of Life Sciences, Nanchang University;2.Jiangxi Poyang Lake National Nature Reserve Authority
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| Abstract: |
| Global climate change models forecast an increase and intensification of extreme flood events in the future. Extreme flooding has profound impacts on functional traits and growth status of submerged macrophytes and the entire ecosystem. Studying the effects of extreme flooding on the growth and development of submerged macrophytes is important for understanding and predicting changes in aquatic ecosystems under the context of climate change. Here, we addressed the dual effects of extreme water level increase and enhanced nutrient loading induced by extreme flood events through setting up four treatments during a 90-day experimental period, including control (water level maintained at 75 cm), two extreme flood regimes (water level increased rapidly from 75 cm to 150 cm on the first day with N and P inputs; the water level increased gradually from 75 cm to 150 cm with N and P inputs), and water level maintained at 75 cm with N and P inputs (the total amount of nutrient input was identical among the latter three treatments). The effects of extreme flooding on the growth, reproductive strategies and biomass allocation of the submerged macrophyte Vallisneria natans were investigated with simultaneous monitoring of phytoplankton, periphyton and nutrient conditions (TN and TP) of the water column. Among the 17 measured indicators of V. natans, only root biomass allocation and sexual reproduction allocation did not change significantly among these four treatments. For the individual effect of water level, both of the two flood regimes (extreme and gradual water level increase) reduced ramet number, leave number, spacer number, total spacer length, maximum root length, number of flowers and fruits, biomass of each organ and the total plant biomass, and promoted the growth of periphyton on artificial stripes compared to the treatment with increased nutrient loading and constant water level. With sudden increase of the water level, the biomass investment in spacers tended to be the lowest, while plant height and the biomass investment in leaves tended to be the highest. For the individual effect of nutrient loading, the significant increase in water column N concentration in the treatment with increased nutrient loading and constant water level promoted the growth of phytoplankton and epiphyton on macrophytes compared to the control treatment. However, in terms of the concentrations of phytoplankton and epiphyton, the shading effect of phytoplankton was relatively greater, which inhibited the growth of plant leaves, roots and spacers, whereas the sexual reproduction biomass remained unchanged. For the pattern of the combined effect of increases in water level and nutrient loading, the combined effect of the two environmental factors would strengthen the effect of water level increase on the growth of submerged macrophytes due to the pulses of nutrient input. The combined effect of the two factors would substantially reduce the biomass of leaves, roots, spacers and sexual organs. Therefore, extreme flooding has a great detrimental effect on submerged macrophytes, including direct effect on water level increase, and indirect effects of the growth and development of submerged macrophytes through promoting phytoplankton biomass. |
| Key words: Submerged macrophyte Vallisneria natans Water level Nutrient loading Phytoplankton Epiphyton |
