铵态氮和浮游植物对穗花狐尾藻的生理影响

Physiological effects of ammonium nitrogen and phytoplankton on Myriophyllum spicatum

为探讨铵态氮-浮游植物-沉水植物三者之间关系,在滇池岸边开展室外模拟实验。在初始叶绿素a为100μg·L-1的浮游植物密度下,研究不同浓度(0、0.05、0.15、0.50、1.50、5.00 mg·L-1)铵态氮和浮游植物对穗花狐尾藻的生长和生理状况的影响。结果表明:各处理组穗花狐尾藻的各项生长和生理指标在实验期间存在明显差异;当铵态氮浓度为1.50mg·L-1时,穗花狐尾藻的株高和生物量明显大于其他处理组;穗花狐尾藻叶片的总叶绿素含量、光合活性和可溶性蛋白在铵态氮浓度为1.50 mg·L-1时,实验期间能维持原来的水平,其余铵态氮浓度下,呈现下降的趋势;在铵态氮与浮游植物的复合作用下,适宜穗花狐尾藻生长的铵态氮浓度为1.50 mg·L-1,高浓度的铵态氮(5.00 mg·L-1)和氮缺乏(NH4+-N≤0.50 mg·L-1)都不利于穗花狐尾藻的生长;铵态氮浓度达到5.00 mg·L-1时,浮游植物大量生长带来的相关效应,如水体浊度上升,水下光强降低等,导致穗花狐尾藻耐受铵态氮的阈值较单一铵态氮胁迫下的耐受阈值低,此时,沉水植物对藻类的抑制效应也将解除,水华大量发生,叶绿素a的浓度可达(948.1±313.0)μg·L-1。

To examine the relationships among ammonium nitrogen(NH4+-N),phytoplankton and submerged macrophytes,an outdoor simulation experiment was conducted on the shores of Dianchi Lake.The effects of NH4+-N on the growth and physiological characteristics of Myriophyllum spicatum were investigated at different NH4+-N concentrations(0,0.05,0.15,0.50,1.50,5.00 mg·L-1)and 100μg·L-1 of the initial chlorophyll-a.The growth and physiological indices of M.spicatum were measured.At the NH4+-N concentration of 1.50 mg·L-1,the height and biomass of M.spicatum were significantly higher than those under other treatments,while the total chlorophyll concentration,photosynthetic activity,and soluble protein concentration of M.spicatum could maintain the initial level.In contrast,these indices decreased in other treatments.Under combined conditions of NH4+-N and phytoplankton,1.50 mg·L-1 of NH4+-N was beneficial to the growth of M.spicatum whereas high concentration of NH4+-N(5.00 mg·L-1)and N deficiency(NH4+-N≤0.50 mg·L-1)were not beneficial to the growth of M.spicatum.When the NH4+-N concentration reached 5.00 mg·L-1,the massive phytoplankton blooms could bring some correlative effects,including the increases of water turbidity and the decreases of underwater light intensity,which resulted in the lower tolerance threshold of M.spicatum compared with single pollution of NH4+-N.Meanwhile,the inhibitory effects of submerged plants on phytoplankton would be relieved,leading to algae blooms,in which the chlorophyll-a concentration reached up to(948.1±313.0)μg·L-1.