不同营养盐条件下赤潮高发区围隔生态系内多胺的变化

Effects of nutrient on polyamines variation in the mesocosm in the East China Sea

在东海赤潮爆发区域运用围隔生态系实验方法,研究了不同营养盐条件下围隔生态系内多胺浓度变化。结果表明:2010年选用东海原甲藻赤潮爆发处海水,东海原甲藻是各围隔生态系内主要优势种,没有种群演替现象发生。两种营养盐添加方式下各围隔内精胺浓度维持较高水平,都呈现先波折下降后波折上升的趋势,与东海原甲藻的生长变化正好相反;各围隔内腐胺浓度水平较高,变化起伏较大,其中有两个实验组腐胺整体变化趋势与东海原甲藻生长趋势类似;所有围隔内亚精胺浓度最低,波动较小。2011年取用中肋骨条藻赤潮爆发处海水,所有围隔生态系内优势种都发生了从中肋骨条藻到东海原甲藻的演替。各围隔生态系内腐胺浓度最高,在中肋骨条藻生长初期腐胺浓度下降,随着中肋骨条藻的生长有所上升,实验后期随着东海原甲藻的生长又整体呈现出下降趋势;各实验组精胺浓度较低,在中肋骨条藻消亡东海原甲藻出现的种群演替期间,都呈现出较大波动;各围隔内亚精胺浓度较低,在整个种群演替过程中没有明显的变化。围隔生态系中补充营养盐,通过对浮游植物生长的影响,间接影响围隔生态系内的多胺变化。

We investigated the effects of different nutrients on the concentration of polyamines by mesocosm experiment in an area of frequent red tide occurrence in the East China Sea. As essential components of cellular regulation, polyamines are synthesized by algae and secreted into the surrounding waters, particularly during the decomposition period following a bloom, and may thus drive the succession of future blooms. In 2010, where blooms of the dinoflagellate Prorocentrum donghaiense occurred, it was the dominant species, the nutrient content of the water was low, and there was no evidence of species succession in any of the mesoeosms. According to our results, P. donghaiense growth period length and maximal biomass would be enhanced with increased levels of nutritive salt, specifically PO4. Polyamines were significantly higher in mesocosms to which nutritive salt was added than in the control mesocosm. Spermine levels showed a wavelike, inverse trend decreasing with P. donghaiense growth and increasing with its decline. Putrescine concentrations were higher than spermine, fluctuated significantly, and were positively associated with growth of P. donghaiense in every mesocosm except the control. Spermidine had the lowest concentration of all the polyamines and fluctuated the least in all mesocosms. In 2011, we detected a succession in species from Skeletonema costatum to P. donghaiense in all mesocosms where S. costatttm blooms occurred. The nutrient content of the seawater, specifically PO4, was sufficient to sustain dinoflagellate populations. However, our results suggest that the addition of NO3 and SiO3 would prolong the S. costatum growth period, and increase its maximal biomass. When just NO3 concentrations were increased, the absorption of PO4 increased significantly, and S. costatum died off more quickly. This suggests that an influx of NO3 could initiate an earlier turnover to P. donghaiense. When more NO3 was added, the maximal biomass of P. donghaiense was higher. If nutrients are added before S. costatum die-off, the rate of turnover might be slower, delaying the appearance of P. donghaiense. In every mesocosm in the second year, putrescine concentration was the most abundant polyamine. In the early growth stages of S. costatum, the level of putrescine initially decreased. Levels then increased with S. costatum growth, and fell again with P. donghaiense growth in the later stages of the experiment. We suggest that S. costatum and P. donghaiense absorb exogenous putrescine, causing it to decrease in the mesocosms. In every mesocosm, spermine concentrations were low and fluctuated greatly during the succession. Similarly, the level of spermidine was low in all microcosms; however, it had no obvious fluctuation during succession. Variation in nutrients affected concentrations of polyamines indirectly by influencing phytoplankton growth. From this 2-year mesocosm experiment, we found that as both S. costatum and P. donghaiense decompose, they release polyamines. We refer to this as the dispersion period. We also found that during growth periods both species metabolize and secrete polyamines. In conditions of lower nutrient availability, exogenous polyamines could stimulate P. donghaiense growth. Algal enzymes catalyze the conversion of polyamines, and thus the growth and decomposition of these dinoflagellates during times of bloom results in significant polyamine fluctuations.