鼠尾藻直立枝光合特性与生长的研究

Study on photosynthetic characteristics and growth of juvenile Sargassum thunbergii

为比较研究鼠尾藻直立枝的顶端、中部和基部光合器官对光能的光合响应机理以及3个部位生长速率与光合作用的联系,用液相氧电极和叶绿素荧光仪分别测定3个部位的净光合放氧速率、暗呼吸速率、快速光曲线、荧光暗弛豫参数;通过培养,比较了3个部位的比生长速率,观察了气囊的产生过程。结果显示,(1)顶端净光合放氧速率和暗呼吸速率显著高于中部与基部(P<0.05)。(2)低光(LL)适应后,叶片重新启动光合作用需要一定的时间,立即照光将会产生光抑制。中光(ML)适应下,叶片光化学反应与热耗散处于平衡态。高光(HL)适应下,叶片实际电子传递速率ETR接近最大值ETRmax,非光化学淬灭(NPQ)显著升高,顶端与中部ETRmax显著高于基部(P<0.05)。(3)LL、ML适应后,叶片暗弛豫较快,HL适应后,暗弛豫较慢。顶端NPQ恢复较快并能完全恢复至0,说明顶端光修复能力较强;而于中、基部较慢且不能恢复至0,表明存在光损伤。(4)顶端色素含量高于中、基部;顶端叶绿素a含量高于类胡萝卜素,而中、基部类胡萝卜素含量高于叶绿素a。(5)3个部位比生长速率为顶端>中部>基部(P<0.05),说明顶端生长最旺盛,有机物质积累较快。狭形叶前端可以裂开形成囊腔,并最终形成气囊,推测温度是主要诱导因素。研究表明,顶端光合作用速率、生长速率和光损伤后的修复能力均高于中、基部。

This study compared photosynthetic characteristics on the tip,middle,base of juveniles Sargassum thunbergii. Parameters analyzed included： net photosynthetic oxygen evolution rate（ Pn）,dark respiration rate（ Rd）,rapid light curve and fluorescent dark relaxation parameters. This was determined using both a liquidphase oxygen electrode system,and pulse amplitude modulated fluorometry. In addition,the growth rate of juveniles was measured by weight,and its relationship with photosynthesis was discussed. The formation of vesicles was observed. The results show that：（ 1） Pnand Rd in the tip were higher than those in the middle and base（ P〈0. 05）.（ 2） In the low light（ LL） adapted samples there was a delay in photosynthesis,and PSⅡ was immediately inhibited if the samples were put in light conditions. However,medium light（ ML）conditions showed photochemical reactions and heat dissipation to be in balance. In high light（ HL）conditions electric transport rate（ ETR） was near saturation,and non-photochemical quenching（ NPQ） was higher than LL and ML conditions. It was also observed that under HL conditions ETRmaxin tip and middle of the juveniles was higher than that in the base（ P〈0. 05）.（ 3） For LL and ML adapted samples,NPQ recovery was fast,whereas in HL it was slow. Under all light levels（ LL,ML,HL） in the samples tip,NPQ recovered rapidly and completely to 0. This indicates highly efficient restoration in the tip,but not in the middle and base where photodamage may be occurring.（ 4） Under ambient light levels pigment content was higher in the tip than that in the middle and base,and Chlorophyll a contents were higher than carotenoid in the tip,which was contrary in the middle and base.（ 5） The specific growth rate values relative to position on the algae were as follows： tip middle base（ P〈0. 05）,indicating fast organic matter accumulation in the tip. It was observed that in increased temperature conditions,small gaps which formed in the narrow leaf tip developed into vesicles. This suggests that temperature is the main inducing factor for the formation of vesicles. The results of this study suggest that photosynthetic rate,growth rate,and recovery capability in the tip of juvenile S. thunbergii may be higher than those in the middle and base.