细基江蓠繁枝变型(Gracilaria tenuistipitata var. liui)铁限制的生理生态学反应

PHYSIOLOGICAL AND ECOLOGICAL RESPONSE OF GRACILARIA TENUISTIPITATA VAR. LIUI TO IRON STRESS

将细基江蓠繁枝变型在铁限制条件下连续培养 6 0天 ,分析海藻体内铁、色素、各种元素 (N、P、C等 )及总氨基酸水平的变化特征、铁限制对细基江蓠繁枝变型光反应系统的影响以及铁限制的细基江蓠繁枝变型对N、P和Fe3+的吸收动力学特征。结果表明 ,在铁限制培养 6 0天过程中 (海水中铁的总浓度为 4 5 1nmol/L) ,细基江蓠组织中铁的含量和色素水平均随着铁限制时间的延长极显著地呈现指数下降。组织铁含量仅为对照组的 5 2 6 % ,叶绿素和藻红素含量分别为对照组的 7 9%和 33 8%。在铁限制培养过程中 ,组织中的N∶P比由起始的 2 9 5 3降低到 2 3 6 8,而C∶N比值几乎保持恒定。比生长率与组织中铁含量呈显著的正相关 ,铁限制使完整组织低温下的荧光发射强度受到不同程度的影响 ,荧光发射峰位蓝移 ,光系统I与光系统II的荧光发射强度之比PSI∶PSII降低。在适度铁限制条件下 (铁限制培养 30天 ) ,细基江蓠对Fe3+的还原和吸收能力都明显增强 ,铁限制海藻铁吸收速率的大小与铁限制的培养过程中以及铁吸收实验过程中介质的氮源种类有关 ,即在以NO- 3 N为惟一氮源进行铁限制培养后 ,在以NH+4 N为氮源的介质中铁的吸收速率远大于在以NO- 3 N为氮源的介质中铁的吸收速率。铁限制在不同程度上影响了细基江蓠对氮。

The total nitrogen (TN),total carbon (TC),total phosphorus (TP) (% DW),pigment,total amino acid and Fe in tissues of Gracilaria tenuistipitata var. liui . were measured during a 60-day period in Fe-stressed condition. Iron content decreased exponentially during Fe-stress to only 5.26% of its original level. TN,TC,TP also decreased,especially the content of TC. The C∶N ratio remained constant while N∶Fe and C∶Fe ratios increased. Total amino acid content decreased after 60 days to 83.7% of its original level. Chl and phycoerythrin (PE) content both declined with decreasing tissue iron content. The absorption spectrum of Chl and PE both reduced,while Fe-stressed cultures induced a blue shift at the fluorescence emission peak (at 436nm and 560nm) and also caused a decreased fluorescence intensity ratio of PSI∶PSII. These results suggested that during the early period of Fe-stressed cultures,PSI may be more sensitive to iron stress than PSII. All the biological uptake kinetics parameters ( V _ max , K_s and a ) of NO -_3,NH +_4 and PO 3- _4 by G. tenuistipitata var. liui decreased under Fe-stressed condition ( especially NO -_3, P < 0.01). The effects of Fe-stress on nutrient uptake rates were in the order of NO -_3>NH +_4>PO 3- _4. The Fe 3+ reduction was conducted using BPDS method and the 55 Fe uptake rate for cultures grown on NO -_3 were measured after re-suspension in either N source NH +_4 or NO -_3 (-Fe,+Fe/NH +_4;-Fe,+Fe/NO -_3). Compared with the control,Fe 3+ 's reduction after Fe-stressed culture for 30 days was faster and,after 60 days of Fe-stress,only a small reduction of Fe 3+ was detectable . Enhanced 55 Fe uptake developed under Fe-stress. During Fe-stress,the highest V _ max appeared in -Fe/NH +_4 45.7 pmol/(mg·h) and the lowest in +Fe/NO -_3 12.3pmol/(mg·h). The requirement for N accelerates further Fe uptake. The growth rate of the algae continued to decline. After 40 days of iron deficiency no further growth was detectable. Chlorosis resulted at the end of the iron stress period. The lower growth rates,chlorosis and even death of the marcoalgae under iron stress were caused by reduced nitrogen utilization,pigment content and photosynthetic capacity.