Litchman E, Klausmeier C A, Yoshiyama K
Kellogg Biological Station, Michigan State University, Hickory Corners, MI 49060, USA.
Proc Natl Acad Sci U S A. 2009 Feb 24;106(8):2665-70. doi: 10.1073/pnas.0810891106. Epub 2009 Feb 6.
Diatoms are key players in the global carbon cycle and most aquatic ecosystems. Their cell sizes impact carbon sequestration and energy transfer to higher trophic levels. We report fundamental differences in size distributions of marine and freshwater diatoms, with marine diatoms significantly larger than freshwater species. An evolutionary game theoretical model with empirical allometries of growth and nutrient uptake shows that these differences can be explained by nitrogen versus phosphorus limitation, nutrient fluctuations and mixed layer depth differences. Constant and pulsed phosphorus supply select for small sizes, as does constant nitrogen supply. In contrast, intermediate frequency nitrogen pulses common in the ocean select for large sizes or the evolutionarily stable coexistence of large and small sizes. Size-dependent sinking interacts with mixed layer depth (MLD) to further modulate optimal sizes, with smaller sizes selected for by strong sinking and shallow MLD. In freshwaters, widespread phosphorus limitation, together with strong sinking and shallow MLD produce size distributions with smaller range, means and upper values, compared with the ocean. Shifting patterns of nutrient limitation and mixing may alter diatom size distributions, affecting global carbon cycle and the structure and functioning of aquatic ecosystems.
硅藻是全球碳循环和大多数水生生态系统中的关键参与者。它们的细胞大小影响碳固存以及向更高营养级的能量传递。我们报告了海洋硅藻和淡水硅藻大小分布的根本差异，海洋硅藻明显比淡水物种大。一个具有生长和养分吸收经验异速生长关系的进化博弈理论模型表明，这些差异可以由氮与磷的限制、养分波动以及混合层深度差异来解释。持续和脉冲式的磷供应会选择较小的尺寸，持续的氮供应也是如此。相比之下，海洋中常见的中频氮脉冲会选择较大的尺寸，或者选择大小尺寸在进化上稳定共存。与大小相关的沉降与混合层深度（MLD）相互作用，进一步调节最佳尺寸，强沉降和浅混合层深度会选择较小的尺寸。在淡水中，与海洋相比，普遍存在的磷限制、强沉降和浅混合层深度导致大小分布的范围、均值和上限值较小。养分限制和混合模式的变化可能会改变硅藻的大小分布，影响全球碳循环以及水生生态系统的结构和功能。
