Competition and facilitation between unicellular nitrogen-fixing cyanobacteria and non-nitrogen-fixing phytoplankton species
Competition and facilitation between unicellular nitrogen-fixing cyanobacteria and non-nitrogen-fixing phytoplankton species
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DOI：
10.4319/lo.2007.52.5.2233
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发表时间：
2007-09-01
影响因子：
4.5
通讯作者：
Huisman, Jef
中科院分区：
文献类型：
--
作者：
Agawin, Nona S. R.;Rabouille, Sophie;Huisman, Jef
最近的发现表明，小型单细胞固氮蓝藻比以前认为的更广泛，可以对海洋的氮预算做出重大贡献。我们结合理论和实验来研究这些小的单细胞固氮生物和其他浮游植物物种之间的氮和光的竞争。我们开发了一个竞争模型，结合了几个生理过程，包括光依赖固氮，硝酸盐同化和固氮之间的切换，和固定氮的释放。在氮限制和光限制恒化器实验中，使用单细胞固氮蓝细菌Cyanothece sp.迈阿密BG 043511、picocyanobacterium Synechococcus bacillaris CCMP 1333和小绿色小球藻Chlorella_ cf sp. CCMP 1227测试模型预测。在单种栽培试验中，通过模型的校正估计了各物种的参数值。随后在一系列的竞争实验中，在不同的硝酸盐水平的模型预测进行了测试。该模型的预测一般与观察到的人口动态。正如预测的那样，在高硝酸盐输入浓度的实验中，具有最低临界光强的物种（S。bacillaris）竞争性地排除了其他物种。在较低的硝酸盐输入浓度下，蓝杆藻的氮释放使蓝杆藻和S.杆菌。更具体地说，模型模拟预测，蓝杆藻的固定氮释放使S。杆菌在物种混合物中的丰度比在单一培养物中的丰度高四倍。这种复杂的相互作用之间的竞争和促进可能是一个主要的决定因素的相对丰度的单细胞固氮蓝藻和非固氮浮游植物物种在贫营养海洋。
Recent discoveries show that small unicellular nitrogen-fixing cyanobacteria are more widespread than previously thought and can make major contributions to the nitrogen budget of the oceans. We combined theory and experiments to investigate competition for nitrogen and light between these small unicellular diazotrophs and other phytoplankton species. We developed a competition model that incorporates several physiological processes, including the light dependence of nitrogen fixation, the switch between nitrate assimilation and nitrogen fixation, and the release of fixed nitrogen. Model predictions were tested in nitrogen-limited and light-limited chemostat experiments using the unicellular nitrogen-fixing cyanobacterium Cyanothece sp. Miami BG 043511, the picocyanobacterium Synechococcus bacillaris CCMP 1333, and the small green alga Chlorella_ cf sp. CCMP 1227. Parameter values of the species were estimated by calibration of the model in monoculture experiments. The model predictions were subsequently tested in a series of competition experiments at different nitrate levels. The model predictions were generally in good agreement with observed population dynamics. As predicted, in experiments with high nitrate input concentrations, the species with lowest critical light intensity ( S. bacillaris) competitively excluded the other species. At low nitrate input concentration, nitrogen release by Cyanothece enabled stable coexistence of Cyanothece and S. bacillaris. More specifically, model simulations predicted that fixed nitrogen release by Cyanothece enabled S. bacillaris to become four times more abundant in the species mixture than it would have been in monoculture. This intricate interplay between competition and facilitation is likely to be a major determinant of the relative abundances of unicellular nitrogen-fixing cyanobacteria and non-nitrogen-fixing phytoplankton species in the oligotrophic ocean.