环境因子及藻体密度对条斑紫菜生长与氮磷去除效率的影响

Abstract

以条斑紫菜为材料,系统探究实验室条件下光照强度、温度、光周期、盐度和干出等生态因子和藻体密度对条斑紫菜生长和氮磷去除的影响,为今后条斑紫菜大规模栽培的生态修复潜力研究及海洋富营养化治理奠定理论基础.实验室条件下不同藻体密度、光照强度、光周期、温度、盐度和干出时间对条斑紫菜生长及氮磷去除效率的影响.结果表明:条斑紫菜在藻体密度0.1 g/L、光照强度为120 μmol m^-2 s^-1时特定生长率最大,为38.1%.随着藻体密度增加,光照强度减小,其特定生长率逐渐减小,当藻体密度为1.6 g/L、光照强度为30 μmol m^-2 s^-1时,特定生长率最小为12.6%;藻体密度0.1-0.8 g/L时随着藻体密度的增加条斑紫菜对NO₃^--N和PO₄^3--P的去除效率显著增加,藻体密度为0.8-1.6 g/L时藻体对NO₃^--N和PO₄^3--P去除效率差异不大,其中藻体密度1.6 g/L、光照强度90 μmol m^-2 s^-1时条斑紫菜对NO₃^--N和PO₄^3--P去除效率均达到93%以上.为进一步探究其他环境因子的影响,因此在温度和光周期实验中选择氮磷去除率适中的藻体密度0.4 g/L和最适光照强度90 μmol m^-2 s^-1.温度为15 ℃、光周期为16L: 8D条件下条斑紫菜特定生长率最大,为36.9%,且氮和磷去除效率也最大,分别为91.9%和81.6%.条斑紫菜生长适宜盐度为10-35,最佳盐度为25,干出时间越长生长越慢,氮磷去效率也越低,且有较大交互作用,但干出后的紫菜光合作用更强.以上研究将为应用大型海藻条斑紫菜大规模栽培进行生态修复奠定基础.;<em> Porphyra yezoensis</em> is an economic marine macroalgae cultivated widely along the coast of the Yellow Sea, China. In this study, the effects of algal density (0.1, 0.2, 0.4, 0.8, and 1.6 g/L), irradiance (30, 60, 90, and 120 μmol m^-2 s^-1), temperature (5, 10, 15, 20 and 25 ℃), photoperiod (8: 16-h, 12: 12-h, and 16: 8-h light: dark: D]), salinity (10, 15, 20, 25, 30, and 35), and desiccation time (0, 1, 2, and 4 h) on the growth and nutrient removal capacity were assessed in the laboratory to study the bioremediation potential of large-scale <em>P</em>.<em> yezoensis</em> cultivation. Each experiment was conducted for 2 weeks. About 3-week-old algae of length 3-5 cm were used. <em>P</em>.<em> yezoensis</em> thalli were grown in gently aerated 250-ml bottles. Von Stosch enrichment (VSE) solution was added to the culture medium containing approximately 500 μmol/L NO₃^--N and 30 μmol/L PO₄^3--P. The culture medium was renewed twice a week; biomass was recorded as the fresh weight and the NO₃^--N and PO₄^3--P contents in the culture medium were measured. The results indicated that the growth rate of <em>Porphyra</em> showed a negative correlation with algal density and a positive correlation with irradiance. In 2 weeks, the maximal algal growth rate of 38.1% was observed, with algal density of 0.1 g/L at an irradiance of 120 μmol m^-2 s^-1. The minimal algal growth rate of 12.6% was observed, with an algal density of 1.6 g/L at an irradiance of 30 μmol m^-2 s^-1. The removal rates of NO₃^--N and PO₄^3--P increased with increasing algal density ranging from 0.1 g/L to 0.8 g/L, whereas no significant differences were noted when the algal density ranged from 0.8 g/L to 1.6 g/L. At an algal density of 1.6 g/L and irradiance of 90 μmol m^-2 s^-1, the maximum NO₃^--N and PO₄^3--P removal rates were 97.3% (1.74 mg N/d) and 93.7% (0.21 mg P/d), respectively. The following conditions were optimal for the growth and nutrition removal: temperature of 15 ℃, photoperiod of 16: 8-h L: D, and salinity of 25. At the above optimal conditions, the maximum growth rate of 36.9% was noted, with the highest NO₃^--N and PO₄^3--P removal efficiencies. However, at 25 ℃ and photoperiod of 8: 16-h L: D, the minimum growth rate of 7.5% was noted, with the lowest NO₃^--N and PO₄^3--P removal efficiency.<em> P</em>. <em>yezoensis </em>could grow in a wide salinity range, from 10 to 35. The maximal growth rate of 37.9%, with the maximum NO₃^--N and PO₄^3--P removal rates of 96.5% (1.70 mg N/d) and 86.9% (0.20 mg P/d), respectively, were observed under 25 salinity and no desiccation (0 h). Although desiccation treatment had a negative effect on the growth and nutrition removal rate, it strengthened the physiological activity. The growth rate and nutrient removal efficiency of no-desiccation groups were higher than those in desiccation groups. Further, low salinity and long desiccation time greatly inhibited algal growth and nutrient uptake; however, the photosynthesis rate in desiccation groups was higher than that in no-desiccation groups. Overall, <em>P</em>. <em>yezoensis</em> showed rapid growth rate, high commercial value, and efficient nutrient concentration, making it an excellent candidate for bioremediation. The study results may be useful for applying <em>P. yezoensis</em> for remediation in coastal waters worldwide.