3种沉水植物碳氮代谢对水体氮源形态组成的响应

Metabolic Characteristics of Three Submerged Macrophytes Exposed to Different NH_4^+-N/NO_3^--N Ratios in Eutrophic Water

以沉水植物穗花狐尾藻(Myriophyllum spicatum L.)、伊乐藻(Elodea canadensis Michx)和金鱼藻(Ceratophyllum demersum L.)为试验对象,研究水体中不同硝态氮(NO_3^-N)和铵态氮(NH_4^+-N)浓度比对植物碳氮(C-N)代谢的影响。2015年春季栽培3种沉水植物;7月,截取长约10 cm的植物顶端于1 L的玻璃烧杯预培养,光暗比为14 L∶10 D,温度控制为光周期25℃,暗周期15℃,光照强度为110μmol/(m^2·s),预培养7 d后截取植物顶端1 g左右转入250 m L的锥形瓶,设计培养液总氮浓度为2 mg/L,按照NH_4^+-N与NO_3^-N的浓度比设置2∶1、1∶1、1∶2、2∶0、0∶2共计5个处理,以预培养液为对照,每个处理设置3个重复。结果表明:(1)与对照相比,氨氮添加显著提高了3种植物组织内游离氨基酸(FAA)的含量,且在氨氮浓度2 mg/L时FAA达最大;(2)植物体内可溶性糖含量(SC)存在显著的种间差异,二元方差分析显示处理间SC的差异,种间差异的贡献值为69%;(3)硝态氮完全替代氨态氮时,3种植物组织中的SC/FAA显著升高,二元方差分析显示处理间SC/FAA的差异主要源于氮源形态组成(56%);(4)伊乐藻体内FAA和SC含量均大于穗花狐尾藻和金鱼藻。这可能是它在富营养水体中更有优势的重要原因之一。

It is known that C-N metabolism in aquatic plants is depressed by high NH4＋ -N concentrations in eu- trophic water. The ratio of soluble carbohydrate to free amino acid （SC/FAA） can be used to index NH4＋ -N stress on C-N metabolism in aquatic plants. In this study, the C-N metabolic characteristics of three submerged plants （ Myriophyllum spicatum L. , Elodea canadensis Michx and Ceratophyllum demersum Linn） grown under different ra- tios of NH4 -N ： NO3--N, with a total dissolved inorganic nitrogen of 2 mg/L （meets Class V water standard） were investigated. The growth rate and levels of FAA and SC of the three aquatic plants were compared to better under- stand the influence of the NH4＋ -N ： NO3- -N ratio on aquatic plant metabolism. Five treatments with varying NH4 - N ： NO3-N ratios （adjusted with NH4C1 and KNO3 ） and one control group were set, with each group run in tripli- cate. The treatments were as follows ： Control, no added NH~＋ -N or NOB -N ; （ 1 ） NH4＋ -N ： NO3 -N = 2 ： 1 ; （2） NH4-N- NO3--N =1 ： 1; （3） NH4-N ： NO3--N=1 ： 2; （4） NH4-N only, no NO-N; （5） NO3--N only, no added NH4-N. The presence of NH4-N significantly increased FAA content in all three plants and the FAA con- tent increased with NH4-N to a minimum of 2 rag/L, the highest treatment level in this study. In the control and the first three treatments, the SC content of the three species were significantly different and two-way ANOVA re- vealed that interspecifie differences accounted for 69% of the observed difference in SC content. When no NH4 -N was added （only NO3--N present） , the SC/FAA ratio in all three species increased significantly and ANOVA indi- cated that the NH4 -N ： NO3- -N ratio contributed 56% to the difference. In addition, E. canadensis Miehx had a higher FAA and SC content than the other two species, which helps explain its growth advantage in eutrophic water bodies.