光强和硝态氮水平对铜藻(Sargassum horneri)生长和光合生理特性的影响

Effects of light intensity and nitrate level on growth and photosynthetic characteristics of Sargassum horneri

以金潮种铜藻(Sargassum horneri)为对象,探讨了不同硝态氮水平下光照强度对其生长和光合生理特性的影响,以期为金潮暴发机制的研究提供一定的参考。实验设置了高(100μmol·L-1)、低(自然海水,50μmol·L-1) 2个硝态氮浓度和高(150μmol photons·m-2·s-1)、中(60μmol photons·m-2·s-1)、低(10μmol photons·m-2·s-1)三个光照水平,检测了藻体在不同硝态氮浓度和光照条件下适应培养7 d后生长、色素含量、可溶性糖含量、可溶性蛋白含量、氮吸收速率及最大光合放氧速率(Pmax)等生理指标的变化。结果表明:氮浓度相同时,铜藻的生长速率、可溶性糖含量、可溶性蛋白含量、氮吸收速率、Pmax均随光照强度的增加而增加,而色素含量随着光照强度的增加而降低;低氮条件下,除类胡萝卜素外,以上指标在高光处理下均显著高于低光处理(P<0.05);高氮条件下,除可溶性糖外,以上指标在高光条件下也均显著高于低光处理(P<0.05);同一光照强度下,色素及可溶性蛋白含量、氮吸收速率及Pmax随氮浓度的增加而增加;可溶性糖含量随着硝态氮浓度的增加而减少;且在3个光照条件下,高氮处理下藻体的Pmax均显著高于低氮处理。总之,不同光照和氮浓度处理7 d后,高光、高氮适应后的藻体表现出较高的生长和光合作用潜能。铜藻断裂后漂浮于海面极易获得较高光强条件,而富营养海水中的高氮条件会刺激铜藻的光合潜能而使其加速生长,进而加剧铜藻金潮的暴发。

The effects of light intensity on the growth and photosynthetic characteristics of Sargassum horneri,a golden tide causing species,were investigated under different nitrate( NO3--N)levels to reveal the physiological mechanism underlying the outbreak of golden tide. There were two NO3--N levels and three light intensities: i.e. high-N( 100 μmol·L-1),low-N( 50 μmol·L-1,the normal NO3-concentration in natural seawater),high-light( 150 μmol photons·m-2·s-1),medium-light( 60 μmol photons·m-2·s-1) and low-light( 10 μmol photons·m-2·s-1). The growth,pigment concentration,soluble sugar concentration,soluble protein concentration,nitrogen absorption rate and the maximum photosynthetic oxygen evolution rate( Pmax) of S.horneri thalli were measured after they had acclimated to different NO3--N and light levels for seven days. The results showed that the growth rate,soluble sugar concentration,soluble protein concentration,nitrogen absorption rate,and Pmaxof S. horneri thalli all increased with increased light intensities,while the pigment concentration decreased with the increasing light intensities.For the low-N acclimated S. horneri thalli,except for carotenoids,all the above mentioned indicators under the high light treatment were significantly higher than those under the low light treatment( P<0.05). For the high-N acclimated ones,except for the soluble sugar,all the indicators under high light treatment were significantly higher than those under the low light treatment( P<0.05). For the S. horneri thalli acclimated under same light intensities,pigment concentration,soluble protein concentration,nitrogen absorption rate and Pmaxincreased with the increasing NO3--N level,while the soluble sugar concentration decreased with the increasing NO3--N level.For the S. horneri thalli acclimated to the three light conditions,the Pmaxunder the high-N treatment was significantly higher than that under the low-N treatment. In conclusion,after seven days acclimation to different light intensities and NO3--N levels,S. horneri thalli showed higher potentials in growth and photosynthesis under the condition of high light intensity and high nitrogen level. Therefore,eutrophication in seawater would aggravate the occurrence of golden tide in that S. horneri thalli can obtain higher light intensities when they break from the stems and drift on the sea surface,which would stimulate the potentials of growth and photosynthesis.