Roselli Leonilde, Basset Alberto
Department of Biological and Environmental Sciences & Technologies, University of Salento, Lecce, Italy.
PLoS One. 2015 May 14;10(5):e0127193. doi: 10.1371/journal.pone.0127193. eCollection 2015.
Understanding the mechanisms of phytoplankton community assembly is a fundamental issue of aquatic ecology. Here, we use field data from transitional (e.g. coastal lagoons) and coastal water environments to decode patterns of phytoplankton size distribution into organization and adaptive mechanisms. Transitional waters are characterized by higher resource availability and shallower well-mixed water column than coastal marine environments. Differences in physico-chemical regime between the two environments have been hypothesized to exert contrasting selective pressures on phytoplankton cell morphology (size and shape). We tested the hypothesis focusing on resource availability (nutrients and light) and mixed layer depth as ecological axes that define ecological niches of phytoplankton. We report fundamental differences in size distributions of marine and freshwater diatoms, with transitional water phytoplankton significantly smaller and with higher surface to volume ratio than marine species. Here, we hypothesize that mixing condition affecting size-dependent sinking may drive phytoplankton size and shape distributions. The interplay between shallow mixed layer depth and frequent and complete mixing of transitional waters may likely increase the competitive advantage of small phytoplankton limiting large cell fitness. The nutrient regime appears to explain the size distribution within both marine and transitional water environments, while it seem does not explain the pattern observed across the two environments. In addition, difference in light availability across the two environments appear do not explain the occurrence of asymmetric size distribution at each hierarchical level. We hypothesize that such competitive equilibria and adaptive strategies in resource exploitation may drive by organism's behavior which exploring patch resources in transitional and marine phytoplankton communities.
理解浮游植物群落组装机制是水生生态学的一个基本问题。在此，我们利用过渡水域（如沿海泻湖）和沿海水域环境的实地数据，将浮游植物大小分布模式解码为组织和适应机制。与沿海水域环境相比，过渡水域的特点是资源可用性更高，水柱混合层更浅且混合良好。据推测，这两种环境之间物理化学状态的差异会对浮游植物细胞形态（大小和形状）施加不同的选择压力。我们以资源可用性（营养物质和光照）和混合层深度作为定义浮游植物生态位的生态轴，对这一假设进行了检验。我们报告了海洋和淡水硅藻大小分布的根本差异，过渡水域浮游植物明显比海洋物种小，且表面积与体积比更高。在此，我们假设影响大小依赖性沉降的混合条件可能驱动浮游植物的大小和形状分布。过渡水域浅混合层深度与频繁且完全混合之间的相互作用可能会增加小型浮游植物的竞争优势，限制大型细胞的适应性。营养物质状况似乎可以解释海洋和过渡水域环境中的大小分布情况，但似乎无法解释在这两种环境中观察到的模式。此外，两种环境之间光照可用性的差异似乎也无法解释在每个层次水平上不对称大小分布的出现。我们假设，这种在资源利用方面的竞争平衡和适应策略可能是由生物体在过渡水域和海洋浮游植物群落中探索斑块资源的行为所驱动的。
