Paerl Hans W
Department of Scientific and Industrial Research, Freshwater Section, Ecology Division, P.O. Box 415, Taupo, New Zealand.
Oecologia. 1979 Jan;38(3):275-290. doi: 10.1007/BF00345188.
In the bloom-forming filamentous blue-green algae Anabaena, both carbon dioxide and nitrogen fixation share a dependence on light. During daylight, A. reduces direct competition between these processes for light-generated reductant by optimizing carbon fixation during late morning hours while optimizing nitrogen fixation during afternoon hours.Sequential optimization was examined from both biochemical and ecological perspectives. Biochemically, it is sound to optimize carbon prior to nitrogen fixation, due to the higher sensitivity of the former to afternoon increases in dissolved oxygen levels which commonly occur in blooms. It is also advantageous to first assure adequate supplies of fixed carbon prior to incorporating fixed nitrogen. Ecologically, the sequence represents optimal use of radiant energy. A. is able to shift energy flow from a highly inhibited to a less inhibited process, thereby maintaining a sink for photo-generated reductant. Both A. and a non-nitrogen fixing diatom community show similar carbon fixation efficiencies during morning and midday hours. During afternoon however, A. diverts significant portions of photo-reductant from carbon to nitrogen fixation. This allows A. to optimize carbon fixation while maintaining access to nitrogen during periods of ambient nitrogen shortage. Accordingly, A. blooms usually appear during summer months when both nitrogen starvation and photosynthetically-active radiation inputs are maximal.
在形成水华的丝状蓝藻鱼腥藻中，二氧化碳固定和固氮都依赖于光。在白天，鱼腥藻通过在上午晚些时候优化碳固定，同时在下午优化固氮，减少了这两个过程对光产生的还原剂的直接竞争。从生化和生态角度对顺序优化进行了研究。从生化角度来看，在固氮之前优化碳固定是合理的，因为前者对水华中常见的下午溶解氧水平升高更为敏感。在纳入固定氮之前，首先确保有足够的固定碳供应也是有利的。从生态角度来看，这种顺序代表了对辐射能的最佳利用。鱼腥藻能够将能量流从高度受抑制的过程转移到抑制较小的过程，从而维持光生还原剂的汇。鱼腥藻和一个不固氮的硅藻群落在上午和中午的碳固定效率相似。然而，在下午，鱼腥藻将大量光还原剂从碳固定转移到固氮。这使得鱼腥藻能够在环境氮短缺期间优化碳固定，同时保持对氮的获取。因此，鱼腥藻水华通常出现在夏季，此时氮饥饿和光合有效辐射输入都最大。
