海黍子对强光的光合响应及适应能力研究

Response and adaptation of Sargassum muticum to light changes

为探讨入侵性海藻海黍子(Sargassum muticum)在漂浮状态下对强光的光合响应及适应能力,使用太阳模拟器模拟出低、中、高3个强光照水平(460、920、1380μmol photons·m^(-2)·s^(-1)),将海黍子在3种强光下暴露2 h后再进行弱光(9.2μmol photons·m^(-2)·s^(-1))恢复4 h。实验期间,分别在0、0.5、1、1.5、2、3、4、5、6 h取样测定藻体最大光化学量子产量(F_(v)/F_(m))、电子传递、非光化学淬灭(NPQ)等叶绿素荧光相关参数及光合色素叶绿素a、叶绿素c含量。结果显示,在强光暴露阶段,海黍子光合活性受到显著抑制(P<0.05):在460、920、1380μmol photons·m^(-2)·s^(-1)3种强光处理后,F_(v)/F_(m)分别较初始状态降低了43.96%、51.15%和76.93%;最大光合电子传递速率(rETR_(max))较初始状态分别降低了36.93%、54.44%、64.84%;单位反应中心吸收、耗散的能量以及捕获用于还原质体醌A(QA)的能量均显著增加(P<0.05),但电子传递受到阻碍。叶绿素a、叶绿素c含量均显著低于初始值,类胡萝卜素含量显著高于初始值(P<0.05)。在弱光恢复阶段,3种强光处理藻体的F_(v)/F_(m)、NPQ、rETR_(max)、光合色素含量均得到不同程度的恢复,低强光处理组(460μmol photons·m^(-2)·s^(-1))藻体相关参数可以恢复到初始状态。研究表明,在强光暴露时海黍子PSII系统反应中心随光强增加受抑制或损坏程度增大。当光强减弱后,海黍子可以通过提高体内类胡萝卜素含量和增强NPQ来消除强光抑制,说明在强光处理后海黍子体内多种保护和恢复机制共同发生了作用。海黍子能够适应白天海水表面较强的光照,在温度、营养盐等其他条件适宜的情况下,漂浮在海面的群体有保持快速生长、并最终发展成为金潮的潜在危害。研究结果可为海黍子金潮暴发的生态机制研究和预警监测工作提供一定的基础数据和理论参考。

Sargassum muticum,one of the invasive species of macroalgae,has invaded the European coast and the Mediterranean region along the Pacific coast,causing serious impacts on local ecosystems and leading to a decrease in local algal biodiversity.More seriously,a large number of drifting individuals of S.muticum have been found on the coast of Lanzarote(Canary Islands),which indicates that this species maybe becomes a potential cause of“golden tide”.S.muticum is an important component of the seaweed bed of the northern China,naturally growing at 2-4 m depth in the subtidal zone.They will receive stronger light when drifting to the surface of seawater.However,research on the physiological response of S.muticum to strong light stress remains unclear.In this study,a solar simulator was used to provide strong light to simulate the actual light density on seawater surface in different seasons.Three strong light levels(460,920,1380μmol photons·m^(-2)·s^(-1))were set,and photosynthetic physiological characteristics of algae were determined after cultivated under different light conditions,to investigate the effects of different levels of light on the photosynthesis of S.muticum.The results showed that the photosynthetic activity of S.muticum was significantly inhibited after 120 min of all three strong light treatments.Compared with the initial state,the maximum photochemical quantum yield(F_(v)/F_(m))was reduced by 43.96%,51.15%and 76.93%,respectively.The maximum photosynthetic electron transfer rate(rETR_(max))was reduced by 36.93%,54.44%,and 64.84%,respectively.The energy absorbed and dissipated per unit reaction center as well as the energy captured for Q A reduction increased significantly with the light level,but electron transfer was hindered.With the light level increasing,the contents of light-trapping pigments reduced,and the inhibition and damage of the reaction center of the PSII system were aggravated in S.muticum.Meanwhile,inhibitions of strong light were alleviated by increasing carotenoid(Car)content and enhancing non-photochemical quenching(NPQ).Car content of S.muticum was elevated by 15.71%,23.81%,and 33.33%respectively,and NPQ was also significantly higher than the initial level.After 240 min of weak light recovery,F_(v)/F_(m),NPQ,rETR_(max),and photosynthetic pigments content of thalli cultured under three strong light levels exhibited different degrees of recovery,and even returned to the initial values in the low-light treatment group(460μmol photons·m^(-2)·s^(-1)).These results indicate that when S.muticum is under strong light stress,multiple protection and recovery pathways could work together to effectively protect or repair the photodamage from light.Therefore,we conservatively speculate that S.muticum may adapt to strong sunlight on sea surface in the daytime,resulting that the drifting population might maintain a rapid growth rate and eventually develop into the golden tide,in case of suitable conditions such as temperature,nutrients,and so on.Our results are expected to provide theoretical and data references for the ecological mechanism research and early warning monitoring work on the golden tide outbreak of Sargassum muticum.