氮负荷升高对苦草(Vallisneria natans)和穗花狐尾藻(Myriophyllum spicatum)生长的影响

Effects of elevated nitrogen loading on the growth of Vallisneria natans and Myriophyllum spicatum

为研究在浅水湖泊的外源污染源控制工作中控氮(N)的必要性,通过室外模拟实验,探究了N负荷升高对浅水湖泊沉水植物生长的影响。实验设置低N组(输入氮磷比为5∶1)和高N组(输入氮磷比为100∶1)两个N负荷水平,同时选择不同生长型的两种沉水植物——莲座型苦草(Vallisneria natans)和冠层型穗花狐尾藻(Myriophyllum spicatum)作为实验对象。结果表明:N负荷升高对苦草生长产生了明显的抑制作用,表现为高N组苦草的相对生长率、生物量、根长、株数和叶片数等指标均显著低于低N组。与苦草不同,N负荷升高对穗花狐尾藻的胁迫作用不显著,两种N浓度下穗花狐尾藻的生物量、相对生长率、节间距、株高和株数均无明显差异。总体而言,N负荷升高显著降低了沉水植物的总生物量,实验结束时高N组沉水植物的总生物量(115.86 g·m^-2)是低N组(321.98 g·m^-2)的36.0%。研究表明,N负荷升高会对沉水植物的生长产生胁迫,但是不同沉水植物对N负荷升高的响应具有种间差异。从湖泊管理和生态修复的角度,本研究支持外源N、P均需要控制的观点。

N and P are key factors that limit phytoplankton growth in freshwater lakes.Controlling external P loading is a widely recognized measure for lake restoration,but the necessity of limiting N inputs remains under debate.Here,we conducted a mesocosm experiment with a duration of 28 d to explore the effects of external N loading on the growth of submerged macrophytes with contrasting growth types of rosette(Vallisneria natans)and canopy(Myriophyllum spicatum).There were mixed plantings of both macrophytes(density ratio:1∶1)in each mesocosm.Our experiment design included one treatment with two levels of N inputs(high N group:N∶P=100∶1;low N group:N∶P=5∶1).The results showed that high N inputs greatly inhibited the growth of V.natans,which had a significantly lower relative growth rate,biomass,root length,and number of plants and leaves in the high N group compared with those in the low N group.However,there were no significant differences in the relative growth rate,biomass,internodal length,total height,and number of plants of M.spicatum between the two N loading treatments,thereby indicating that N loading did not have a significant effect on the growth of M.spicatum.Overall,the total biomass of the two submerged macrophytes in the high N group(115.86 g·m^-2)was only 36.0%of that in the low N group(321.98 g·m^-2),thereby indicating that high external N loading had a significant negative effect on submerged macrophytes.Our study suggested that high N inputs can greatly reduce submerged macrophytes in shallow lakes,but the effects are species-specific.From the perspective of lake management and restoration,our study supported the view that both N and P should be controlled.