State Key Laboratory of Estuarine and Coastal Research, School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China.
State Key Laboratory of Estuarine and Coastal Research, School of Ecological and Environmental Sciences, East China Normal University, Shanghai 200241, China
J Exp Biol. 2019 Apr 24;222(Pt 8):jeb197947. doi: 10.1242/jeb.197947.
The metabolism of a living organism (e.g. bacteria, algae, zooplankton) requires a continuous uptake of nutrients from the surrounding environment. However, within local spatial scales, nutrients are quickly used up under dense concentrations of organisms. Here, we report that self-spinning dinoflagellates sp. (clade E) generate a microscale flow that mitigates competition and enhances the uptake of nutrients from the surrounding environment. Our experimental and theoretical results reveal that this incessant active behavior enhances transport by approximately 80-fold when compared with Brownian motion in living fluids. We found that the tracer ensemble probability density function for displacement is time-dependent, but consists of a Gaussian core and robust exponential tails (so-called non-Gaussian diffusion). This can be explained by interactions of far-field Brownian motions and a near-field entrainment effect along with microscale flows. The contribution of exponential tails sharply increases with algal density, and saturates at a critical density, implying a trade-off between aggregated benefit and negative competition for the spatially self-organized cells. Our work thus shows that active motion and migration of aquatic algae play key roles in diffusive transport and should be included in theoretical and numerical models of physical and biogeochemical ecosystems.
生物（如细菌、藻类、浮游动物）的新陈代谢需要从周围环境中持续摄取营养物质。然而，在局部空间尺度上，在生物密集的情况下，营养物质很快就会被耗尽。在这里，我们报告说，自旋转甲藻属 sp.（E 类群）会产生微尺度流，从而减轻竞争并增强对周围环境中营养物质的吸收。我们的实验和理论结果表明，与活体液中的布朗运动相比，这种持续的主动行为将运输增强了约 80 倍。我们发现，示踪剂总体概率密度函数的位移随时间变化，但由高斯核和稳健的指数尾巴（所谓的非高斯扩散）组成。这可以通过远场布朗运动和近场夹带效应以及微尺度流的相互作用来解释。指数尾巴的贡献随着藻类密度的增加而急剧增加，并在临界密度处饱和，这意味着在空间自组织细胞的聚集效益和负面竞争之间存在权衡。因此，我们的工作表明，水生藻类的主动运动和迁移在扩散传输中起着关键作用，应该被纳入物理和生物地球化学生态系统的理论和数值模型中。
