氮磷比对有机磷环境中微藻砷代谢的生态风险效应

Effect of N/P ratio on ecological risk of arsenic metabolism of microalgae in the presence of organic phosphorus

摘要:

【目的】探究了以单酯磷d-葡萄糖-6-磷酸二钠（d-glucose-6-disodium phosphate，GP）为唯一磷源时含砷（As⁵⁺）水体中不同氮磷质量比对铜绿微囊藻（Microcystis aeruginosa）生长及砷代谢和微囊藻毒素（microcystins，MCs）释出的影响。【方法】将氮磷饥饿状态的藻细胞于含砷水体中不同氮磷比条件下进行实验，通过测定藻细胞密度（OD₆₈₀）、叶绿素a （chlorophyll a，Chla）、实际光合产率（Yield）、超氧化物歧化酶（superoxide dismutase，SOD）、砷的存在形态以及微囊藻毒素含量，分析该藻在砷胁迫下的生理响应以及砷代谢机制。【结果】氮磷饥饿状态藻细胞对较高GP水平（0.1 mg/L）下的低氮磷比有更好的适应性，较低GP水平（0.02 mg/L）下的高氮磷比能显著促进培养初期藻细胞的OD₆₈₀、Chla和Yield；SOD在培养初期与末期受氮磷比影响显著。GP环境下铜绿微囊藻经8 d培养后氮磷比为10：0.1介质中的砷表现为以亚砷酸盐（As³⁺）为主，占水体总砷（total arsenic，TAs）含量的78.8%，其余氮磷比环境中仍以As⁵⁺为主，藻体砷形态则均以As⁵⁺为主，氮磷比为1：0.1时有机砷占藻体TAs比例最高。藻细胞砷代谢受GP水平影响显著，较高GP环境（0.1 mg/L）下砷的代谢总量也更高，氮磷比为10：0.1时砷代谢以As⁵⁺的还原和As³⁺释出为主，低GP环境下（0.02 mg/L）砷代谢的甲基化水平提高。介质中MCs的含量与GP水平有关，较高GP的低氮磷比水体中MCs含量最低。【结论】研究结果对全面了解有机磷源含砷水体中藻华暴发及砷生态风险的科学管控具有重要意义。

Abstract:

[Objective] To explore the effect nitrogen/phosphorus (N/P) ratio on growth, arsenic (As) metabolism, and microcystins (MCs) release of Microcystis aeruginosa in arsenate (As⁵⁺)-polluted water when d-glucose-6-disodium phosphate (GP) was the only phosphorus source. [Methods] The experiment was carried out on N- and P-starved algal cells in As-containing water with different N/P ratios. The algal cell density (OD₆₈₀), chlorophyll a (Chla), actual photosynthetic yield (Yield), superoxide dismutase (SOD) activity, and the content of As species and MCs were measured. Thereby, the physiological response of M. aeruginosa to As stress and the metabolic pathways of As were analyzed. [Results] The N- and P-starved algal cells can well adapt to the low N/P ratio in the case of high GP level (0.1 mg/L), and high N/P ratio in the instance of low GP level (0.02 mg/L) can significant improve the OD₆₈₀, Chla, and Yield of the algal cells in the early stage of culture. The effect of N/P ratio on SOD activity was more significant at the beginning and end of culture. After 8 days of culture, arsenite (As³⁺) changed into the dominant As species in the medium with N/P ratio of 10:0.1, which made up 78.8% of the total As (TAs) in the water, but As⁵⁺ was still the main As species in the media with other N/P ratios. Meanwhile, As⁵⁺ was the dominant As species in algal cells for different N/P ratios, and in the case of N/P ratio at 1:0.1, the proportion of organic As in TAs in algal cells was the largest. As⁵⁺ metabolism in M. aeruginosa cells was significantly affected by GP level, and the high amount of metabolized As per cell was found in the instance of high GP level (0.1 mg/L). In the case of N/P ratio of 10:0.1, As metabolism was dominated by the reduction of As⁵⁺ and the release of As³⁺, and methylation level of As was elevated in the case of low GP level (0.02 mg/L). The concentration of MCs in the medium was related to GP level and the concentration was the lowest in the case of low N/P ratio and high GP level. [Conclusion] The results are of great significance for comprehensive understanding of harmful algal blooms and scientific management of As in As-polluted water under organic phosphorus conditions.