The silica frustules of diatom are regarded as an important physical defense against predation. While the biogenic silica content of diatoms is a major factor controlling the ingestion rate of copepods, how it affects the three-dimensional structure and the mechanical properties of the frustules, and consequently copepod grazing, has not been studied. In this study, the diatoms Thalassiosira weissflogii and Amphora coffeaeformis were grown under different light intensities to manipulate their cellular biogenic silica contents. This manipulation generated diatom cells with distinct nano-structures and mechanical strengths. The diatoms were then fed to the copepod Paracalanus pravus to test the effect of biogenic silica contents on copepod feeding. We demonstrated that the copepods preferred the low-silica cells of T. weissflogii, but showed a preference for the high-silica cells of A. coffeaeformis. Atomic force microscopy and X-ray photoelectron spectroscopy analyses revealed that the chemical composition and mechanical properties of diatom frustules varied with silica contents. High silica containing T. weissflogii had higher frustule elasticity and hardness. In contrast, A. coffeaeformis containing more biogenic silica had lower frustule elasticity but silica level had little effect on the hardness of the frustule. Our results indicate that the nano-structure and chemical properties of the frustules determine the mechanical strength of the diatom frustules. This nanoscale study improves our understanding of the relationship between diatom biogenic silica content and copepod grazing in marine planktonic food webs.

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不同二氧化硅含量的硅藻壳由于纳米级机械性能的差异而影响桡足类放牧

硅藻的硅藻壳被认为是抵御捕食的重要物理防御。虽然硅藻的生物二氧化硅含量是控制桡足类摄食率的主要因素，但它如何影响硅藻壳的三维结构和机械性能，进而影响桡足类吃草，尚未得到研究。在这项研究中，硅藻Thalassiosira weissflogii和Amphora coffeaeformis在不同的光照强度下生长，以控制它们的细胞生物二氧化硅含量。这种操作产生了具有独特纳米结构和机械强度的硅藻细胞。然后将硅藻喂给桡足类Paracalanus pravus测试生物二氧化硅含量对桡足类进食的影响。我们证明桡足类更喜欢T. weissflogii的低二氧化硅细胞，但显示出对A. coffeaeformis的高二氧化硅细胞的偏好。原子力显微镜和 X 射线光电子能谱分析表明，硅藻壳的化学成分和机械性能随二氧化硅含量而变化。含硅量高的T.weissflogii具有较高的硅藻壳弹性和硬度。相比之下，A. coffeaeformis含有较多生物二氧化硅的硅藻壳弹性较低，但二氧化硅含量对硅藻壳硬度影响不大。我们的结果表明硅藻壳的纳米结构和化学性质决定了硅藻壳的机械强度。这项纳米级研究提高了我们对海洋浮游食物网中硅藻生物二氧化硅含量与桡足类放牧之间关系的理解。