水华束丝藻对磷的生理响应研究

PHYSIOLOGICAL RESPONSE TO PHOSPHOURS IN APHANIZOMENON FLOS-AQUAE

束丝藻(Aphanizomenon Morr.ex Born.et Flah.)是我国淡水水体常见的水华蓝藻之一,由其引发的水华已产生了严重的环境及生态安全问题。然而,目前对束丝藻的研究仍相对较少。为了揭示环境因子对束丝藻的影响,研究从淡水水体限制因子?磷入手,探讨其对束丝藻的生理生态效应,研究了不同磷浓度(0.00、0.02、0.05、0.50、1.00 mg/L)对水华束丝藻的生长、光合作用及碱性磷酸酶变化的影响。结果表明:水华束丝藻在磷浓度低于0.50 mg/L条件下,其比生长速率(μ)、最大光合反应(Pm)、饱和光强(Ik)、PSⅡ光化学效率(Fv/Fm)和最大电子传递速率(ETRmax)均下降,而暗呼吸(Rd)显著增加,这表明培养基磷浓度低于0.50 mg/L时,水华束丝藻产生磷营养胁迫,导致其光合作用受到抑制,呼吸作用增强,进而抑制其生长。为了应对这种胁迫,束丝藻显著增加了其碱性磷酸酶活性(APA),APA的增加,使得水华束丝藻能够分解有机形态磷物质转化为其可利用无机磷来缓解磷胁迫。当磷浓度高于0.50 mg/L时,水华束丝藻各种参数并没显著性差异,表明磷浓度高于0.50 mg/L能够保证水华束丝藻的正常生理特征。这些结果揭示了在低磷条件下,水华束丝藻能通过调节光合作用和APA等生理响应,使其保持生存和竞争优势。

Aphanizomenon sp.is one of the most common bloom-forming cyanobacteria in Chinese freshwater bodies.The bloom,formed by Aphanizomenon,has resulted in serious environmental and ecological safe problems.Therefore,owing to its potential effect,directly or indirectly,on animal and human,Aphanizomenon has attracted great attention by researchers and managements.As already illustrated,many bloom-forming cyanobacteria have developed some sound ecological strategies to form water bloom during evolution,while the mechanism in Aphanizomenon remains still un-known.The increase of phosphorus concentration,a limiting factor at freshwater bodies,is always thought to be re-sponsible to the bloom formation.However,there are relatively few data to study how to respond to the increase of phosphorus levels in Aphanizomenon at present.Therefore,in order to explain the responses to phosphorus in Apha-nizomenon,the physiological and ecological functions of Aphanizomenon were selected to discuss in the present study.In this study,the physiological parameters,including the specific growth rate,photosynthesis evolution,maximum elec-tron transfer rate（ETRmax） and alkaline phosphatase activities（APA）,were investigated when Aphanizomenon flos-aquae,a type strain of Aphanizomenon,was cultured at different phosphorus concentrations（0.00,0.02,0.05,0.50 and 1.00 mg/L）.The results showed that significant decreases were found in the specific growth rate（μ）,the maximum photosynthesis rate（Pm）,saturation light irradiance,PSⅡphotochemical efficiency（Fv/Fm）,and the maximum electron transfer rate（ETRmax）,when A.flos-aquae was inoculated into the Pi levels of less than 0.50 mg/L.On the contrary,significant in-creases were indicated in the respiration（Rd） of Aphanizomenon when cultured at lower Pi concentrations.It suggested that Pi stress was found in A.flos-aquae when grown at less than 0.50 mg/L Pi concentration,and the stress might di-rectly inhibit photosynthesis efficiency,which resulted in the increase of respiration and the decrease of growth.At the same time,A.flos-aquae increased markedly its activity of alkaline phosphatase（APA） in order to response to the stress since alkaline phosphatase could translate organic phosphate into inorganic phosphate.When cultured at higher Pi con-centration more than 0.50 mg/L,the physiological parameters did not markedly change,suggesting that A.flos-aquae could keep a normal growth rate only when the Pi levels reached to 0.50 mg/L or higher.In conclusion,the data sug-gested that A.flos-aquae could regulate its physiological responses,such as photosynthesis and APA activities,and so on,to deal with Pi stress in order to keep its survival and dominance.