不同浓度氨氮对4种沉水植物的生长影响比较研究

Comparison of Effects of Ammonia-nitrogen Concentrations on Growth of Four Kinds of Submerged Macrophytes

选取轮叶黑藻(Hydrilla verticillata)、苦草(Vallisneria natans)、金鱼藻(Ceratophyllum demersum)、小茨藻(Najas minor)4种沉水植物为研究对象,在实验室静态模拟条件下,通过定期测定植物生物量、叶绿素、可溶性糖、过氧化物酶等指标变化,比较研究了不同浓度氨氮对4种沉水植物的生长影响。研究结果表明,本研究条件下,轮叶黑藻、苦草、金鱼藻、小茨藻的氨氮最大适宜浓度和最大耐污浓度分别为2、2、1、0.5 mg·L^(-1)和6、6、4、2 mg·L^(-1)。不同沉水植物的相对生长率均随着水体氨氮浓度的升高呈现先上升后下降的变化规律,轮叶黑藻、苦草、金鱼藻和小茨藻均在相应的氨氮最大适宜浓度时出现相对生长率最大值,其值分别为1.21、0.94、0.52和0.28。不同沉水植物在相应的氨氮最大适宜浓度范围内,试验期间植物的叶绿素和可溶性糖含量呈现上升趋势,植物的POD活性变化不大;当水体氨氮介于相应的最大适宜浓度和最大耐污浓度之间时,试验期间植物的叶绿素和可溶性糖含量变化规律不明显,植物的POD活性显著高于CK处理;当水体氨氮浓度超过相应的最大耐污浓度时,试验期间沉水植物叶绿素和可溶性糖含量呈下降趋势,植物的POD活性在7~21 d达到最大值,之后开始下降。研究表明,水体氨氮浓度是影响沉水植物生长的限制因素之一,不同沉水植物均存在相应的氨氮最大适宜浓度和最大耐污浓度,相应的低浓度氨氮能促进沉水植物生长,沉水植物均存在不同程度的抗逆能力,但过高浓度氨氮会抑制沉水植物生长,甚至导致死亡。

Four local submerged macrophytes of Hydrilla verticillata, Vallisneria natans, Ceratophyllum demersum and Najas minor were chosen to investigate the effects of ammonia-nitrogen（NH4^＋-N）on their growth by measuring their biomass, chlorophyll contents, soluble sugar contents and peroxidase（POD） activities. The results indicated that the maximum optimum concentrations（MOCs） of ammonia-nitrogen for Hydrilla verticillata, Vallisneria natans, Ceratophyllum demersum and Najas minor were 2, 2, 1 mg·L^-1 and 0.5 mg·L^-1 respectively, while the maximum tolerant concentrations（MTCs）were 6, 6, 4 mg·L^-1 and 2 mg·L^-1. The relative growth rate of different submerged macrophytes showed the trend of increasing first followed by decreasing with the elevated ammonia-nitrogen levels. The maximum relative growth rates of Hydrilla verticillata, Vallisneria natans, Ceratophyllum demersum and Najas minor occurred at the MOCs of NH_4~＋-N,with the values of 1.21, 0.94, 0.52 and 0.28, respectively. Chlorophyll contents and soluble sugar contents in different submerged macrophytes had an increasing trend at the range of MOCs of NH4^＋-N, while there was no significant changes for POD activities. Meanwhile,chlorophyll contents and soluble sugar contents changed not significantly, and POD activities were significantly higher than CK, while aquaticammonia-nitrogen concentration was between MOC and MTC. When aquatic NH4^＋-N was beyond MOT, chlorophyll conents and soluble sugar contents decreased, and POD activities reached the maximum values at 7 ~21 d and then decreased since then. It can be concluded as follows：aquatic NH4^＋-N is one of the limiting factors on affecting growth of submerged macrophytes and different types have their corresponding MOC and MTC; Low NH4^＋-N concentrations can promote growth of submerged macrophytes due to their resistance ability,while high levels may inhibite their growth and even leads to death.