不同浓度铵态氮对苦草的生理影响

研究了苦草在不同浓度(0.02,0.05,0.10,0.30,0.60,1.00,3.00mg/L)铵态氮中暴露14d后,其生物量的变化、叶片游离氨基酸态氮、叶绿素、可溶性蛋白含量以及O2-×信号强度、抗氧化酶活性和丙二醛(MDA)含量的响应.结果表明,各浓度组苦草的生物量无显著变化,但是各生理指标变化显著.当铵态氮浓度为0.30mg/L时,苦草叶片中游离氨基酸态氮的含量即开始显著升高.当铵态氮浓度达到0.60mg/L时,超氧化物歧化酶(SOD)活性显著升高,表明苦草诱导产生氧化应激但未受到氧化损伤.当铵态氮浓度高于1.00mg/L时,SOD和过氧化物酶(POD)活性显著升高,O2-×信号强度显著增强,叶绿素、可溶性蛋白含量显著降低.当铵态氮浓度为0.02mg/L时,O2-×信号强度显著增强.综上,铵态氮浓度低于0.60mg/L苦草生长良好,浓度31.00mg/L苦草光合能力受到抑制、代谢受到干扰.苦草对铵态氮最敏感的生理生化指标是叶片中游离氨基酸态氮含量.铵态氮作为沉水植物的一种营养物质,当其含量较低时,植物由于营养缺乏诱导产生自由基.

Physiological effect of Vallisneria natans L.under different concentrations of ammonia

The effects of biomass, nitrogen in free amino acids, chlorophyll, soluble proteins and malondialdehyde(MDA), intensities of O2-× and antioxidant enzyme activities in the leaves of Vallisneria natans L. exposed to different concentrations of NH4+-N (0.02,0.05,0.10,0.30,0.60,1.00,3.00mg/L) after 14 days were investigated. No significant changes were observed for the biomass of leaves in the studied exposing level, while the physiological signals showed different trends. Intensities of O2-× increased at the lowest concentration of ammonia(0.02mg/L). The nitrogen contents in the free amino acids started to increase significantly from 0.30mg/L NH4+-N. When the NH4+-N reached 0.60mg/L, SOD activities were significantly induced, indicating oxidative stress to the plant without oxidative damage. When the ammonia concentrations were higher than 1.00mg/L, the signal intensities of free radicals and activities of SOD and POD significantly increased, while the contents of chlorophyll and soluble protein decreased, indicating oxidative damage might happen. Generally, the plants grew well when the NH4+-N concentration was below 0.60mg/L and stress and growth disturbance happened when it was above 1.00mg/L. Among all those physiological parameters measured, the nitrogen content in the free amino acids in the plant leaves was the most sensitive indicator. Results also suggested that deficiency of nutrient at a low level of ammonia may cause the induction of free radicals in submerged plant leaves.