凤眼莲入侵程度对金鱼藻和黑藻生长及种间关系的影响

湿地生态系统中凤眼莲（Eichhornia crassipes）入侵造成湿地植物群落结构退化及功能崩溃，直接影响沉水植物的生长繁殖及初级生产力。目前关于凤眼莲的入侵机制有一定的研究，而关于凤眼莲入侵程度对沉水植物金鱼藻（Ceratophyllum demersum）和黑藻（Hydrilla verticillate）生长及种间关系的影响相对缺乏。以外来入侵植物凤眼莲，沉水植物金鱼藻和黑藻为研究对象，设计凤眼莲入侵程度（无入侵，轻度入侵对应盖度25%，重度入侵对应盖度75%）交叉定植方式（黑藻单种模式、金鱼藻单种模式，金鱼藻和黑藻混种模式）的控制实验，探究凤眼莲入侵强度对沉水植物金鱼藻和黑藻生长及种间关系的影响。结果表明，凤眼莲入侵程度显著降低了金鱼藻的生物量、分枝数；黑藻的株高、分枝数和分节数。无凤眼莲入侵时，两种沉水植物生物量均最大，两者种间竞争关系较强；随凤眼莲入侵盖度增加，两种沉水植物的生物量先急剧降低后略微增加，种间关系经过微弱促进后又变为竞争作用，其中黑藻表现出明显的竞争优势。此外，凤眼莲入侵略微降低了水体中的总氮、总磷含量。结构方程模型分析结果表明凤眼莲入侵以及水体总氮、总磷等水体理化性质对沉水植物生长均有显著负向影响（P<0.05），且水体理化性质对沉水植物生长的影响强于凤眼莲入侵。总之，凤眼莲入侵显著降低了金鱼藻和黑藻生长繁殖，随着凤眼莲入侵程度增加，两种沉水植物种间关系由竞争转变为促进再转变为竞争。研究结果为凤眼莲入侵有效控制及湿地沉水植被的恢复与重建提供了一定的理论依据和技术支撑。

Effects of Eichhornia crassipes invasion degree on the growth traits and inter-specfic relationship between Ceratophyllum demersum and Hydrilla verticillata

Biological invasion has become the destruction of wetland ecosystem, and it is becoming more and more serious ecological problems. Alien invasive species can occupy a wide space in a short period of time and reproduce rapidly, which causes the changes in the characteristics and disappearance, and even extinction of local species. At last it would destroy the stability of the ecosystem. The invasion of Eichhornia crassipes in the wetland ecosystem results in the simplification and degradation of the aquatic plant community structure and function, which leads to the imbalance of the aquatic ecosystem and primary productivity decrease of submerged plant. Submerged plants are the important primary producers in many aquatic ecosystems, such as lakes and rivers. They play an important role in the health and stability of wetland ecosystems, and are also commonly used in wetland restoration projects. At present, there are some researches on the invasion mechanism of E. anemonis, but the effects of invasion degree on the growth and interspecies relationship of submerged plants Ceratophyllum demersum and Hydrilla verticillate are relatively lack. In this research, the effects of E. crassipes invasion degree on the growth and interspecific relationship of C. demersum and H. verticillata were explored in the control experiment. The results indicated that the biomass and branches of C. demersum and H. verticillata significantly decreased with the increase of the coverage of E. crassipes. The total biomass of submerged macrophytes was the greatest in the absence of E. crassipes. The interspecific competitive relationship between the two submerged plants was the strongest in the absence of E. crassipes, and with the coverage of E. crassipes rise, the relationship between the two submerged plants become competitive from week beneficial. H. verticillata had a significantly competitive advantage when they grew with C. demersum. Furthermore, the total nitrogen (TN) and total phosphorus (TP) contents in water were slightly decreased by the invasion of E. crassipes. Structural equation model (SEM) analysis results showed that plant invasion and water physical and chemical properties including TN and TP had a significantly negative impact on the growth of the submerged plants (P<0.05), the correlation between the physical and chemical properties of water and the growth of submerged plants was more significant. In conclusion, E. crassipes invasion degree significantly reduced the growth and reproduction of the two submerged plants. With the increase of invasion degree, the relationship between the two submerged species became from competition to assistance and then to competition. The results provide theoretical basis and technical support for the effective control of the invasion of E. crassipes and the restoration and reconstruction of submerged vegetation in wetland.