不同氮素对冠盘藻生长和光合荧光特性的影响

Effects of Nitrogen on the Growth and Chlorophyll Fluorescence of Stephanodiscus hantzschii

硅藻水华广泛存在于富营养化水体中,常造成恶劣的环境影响,氮素输入是造成硅藻水华现象的主要因素之一。为明确氮素营养对硅藻水华的影响,揭示其对氮素的响应机理,以常见硅藻水华优势种冠盘藻(Stephanodiscus hantzschii)为研究对象,分别以硝酸钠、氯化铵和尿素作为氮源,分析了不同氮素条件下冠盘藻生长和叶绿素荧光参数(F_(v)/F_(m)、α、I_(k)、ETR_(max))的变化特征。结果显示,不同形态氮素对冠盘藻的生长及叶绿素荧光参数影响显著,一定程度上提高水体氮素浓度能够提升冠盘藻的叶绿素荧光,促进其生长。相比于氨氮和尿素,硝氮营养更有利于冠盘藻的生长,高浓度硝氮条件下,冠盘藻生长良好,而氨氮浓度大于5 mg/L、尿素浓度达到10 mg/L时,冠盘藻叶绿素荧光参数显著降低,生长受到抑制。较高浓度氨氮及尿素对冠盘藻叶绿素荧光参数的抑制作用主要发生在其生长的前中期,随着氮素消耗,冠盘藻的光合参数F_(v)/F_(m)、Ik、ETR_(max)均随氮素浓度的增加而增加,低氮条件下的冠盘藻会提高α值来增大对光能的利用效率,从而提高其环境适应性。研究表明,氮素一定程度上能够通过影响冠盘藻的光合作用而影响其在水环境中的生长。

Diatom blooms are a common phenomenon in eutrophic water bodies.The blooms adverse-ly affect the environment,and excessive inputs of nitrogen is a primary factor leading to diatom blooms.Stephanodiscus hantzschii is widely distributed in lakes,rivers,and reservoirs,and has been the dominant species in diatom blooms reported at home and abroad.In this investigation,S.hantzschi was selected for study,and we explored different concentrations and forms of nitrogen (sodium nitrate ammonium chloride and urea) on the growth and chlorophyll fluorescence parameters of S.hantzschi using indoor simulation experiments.Our focus was on the specific growth rate,chlorophyll a concen-tration,and the following fluorescent parameters:maximum photochemical efficiency (F_(v)/F_(m)),ligh use efficiency (α value),half-saturation light intensity (I_(k)) and maximum electron transport rate(ETR_(max)).The aim was to reveal the nitrogen response mechanism of diatoms and provide a reference for controlling algal blooms.Five nitrogen concentrations (0.5,1,2,5,10 mg/L) were set for each of the three nitrogen sources,with each treatment in triplicate.The algal cell density,chlorophyll a con-centration and chlorophyll fluorescence parameters of each treatment were determined every two days during the 21-day experiment.Results show that the growth and chlorophyll fluorescence parameters of S.hantzschii varied significantly with treatment (nitrogen source).Higher nitrogen concentrations to a degree that depended on the form,promoted the growth and improved chlorophyll fluorescence of S.hantzschii.The specific growth rate of the sodium nitrate treatment group was highest,followed by the urea group and ammonium chloride group.The specific growth rates of sodium nitrate groups with nitrogen concentrations of 0.5 mg/L,1.0 mg/L and 10 mg/L were all higher than those of the ammonium chloride and urea groups with the same nitrogen concentrations.The specific growth rate for the 10 mg/L nitrate-N treatment group reached 0.124,which was 46.1%higher than the ammo-nium chloride group and 19.4%higher than the urea group.Nitrate clearly promotes the growth of S.hantzschii better than ammonia or urea.Further,a nitrogen concentration exceeding 5 mg/L in the form of ammonium chloride or 10 mg/L in the form of urea,significantly reduced the chlorophyll fluo-rescence parameters and growth of S.hantzschii,and the reduction in photosynthetic parameters occurred in the early and middle growth stages.In addition,we found that S.hantzschii adapted to nitrogen deficiency by increasing the utilization efficiency of light energy (i.e.,theαvalue increased at low nitrogen concentrations).To summarize,the concentration of nitrogen in water affects the photo-synthesis of S.hantzschii,consequently affecting its growth.