This study elucidates the effect of colony formation on light absorption by Botryococcus braunii microalgae cells. The spectral average mass absorption cross-section of suspensions of B. braunii cultures with free-floating cells or colonies was measured experimentally across the photosynthetically active radiation region. The average mass absorption cross-section was found to decrease significantly across the spectrum in the presence of colonies. This observation could be attributed to (i) reduced pigment concentrations due to nutrient limitations, (ii) mutual shading of the aggregated cells, and/or (iii) the presence of the colonies' extracellular matrix. The Monte Carlo ray tracing method was used to elucidate the contribution of each of these phenomena on the mass absorption cross-section of cells in colonies. Colonies were modeled either as fractal aggregates of monodisperse cells or as an ensemble of monodisperse cells regularly arranged at the periphery of a hollow sphere embedded in a spherical extracellular matrix or as a volume and average projected area equivalent coated sphere. The change in pigment concentrations due to nutrient limitation was found to be the most important factor. In addition, the mass absorption cross-section of cells in colonies was found to decrease due to mutual shading among cells. This effect was stronger with increasing number of cells in the colony and increasing cell absorption index. The effect of extracellular matrix on the mass absorption cross-section was found to be negligible. Finally, good agreement was found between the equivalent coated sphere approximation and the colonies modeled as fractal aggregates comprised of monodisperse cells. This study also established that the Monte Carlo ray tracing method can be used for a variety of microalgae species and colony configurations, whose absorption cross-section are not readily calculated by standard methods due to their complex geometry, inhomogeneous nature, and large size compared to the wavelength of the incident light.

这项研究阐明了菌落的形成对Botryococcus braunii微藻细胞吸收光的影响。布鲁氏杆菌悬浮液的光谱平均质量吸收截面在光合作用的辐射区域内，通过实验测量了具有自由漂浮细胞或菌落的培养物。发现在存在菌落的情况下，整个质谱的平均质量吸收横截面显着降低。该观察结果可归因于（i）由于营养限制而降低的色素浓度，（ii）聚集细胞的相互遮蔽，和/或（iii）菌落的细胞外基质的存在。蒙特卡罗射线追踪法用于阐明每种现象对菌落细胞质量吸收截面的贡献。将集落建模为单分散细胞的分形聚集体，或建模为规则排列在嵌入球形细胞外基质的空心球外围的单分散细胞集合，或建模为体积和平均投影面积等效的涂层球体。发现由于营养限制而导致的色素浓度变化是最重要的因素。另外，发现由于细胞之间的相互遮蔽，菌落中细胞的质量吸收截面减小。随着菌落中细胞数量的增加和细胞吸收指数的增加，这种作用更强。发现细胞外基质对质量吸收横截面的影响可忽略不计。最后，在等效涂层球面近似与以单分散细胞组成的分形聚集体建模的菌落之间发现了很好的一致性。这项研究还确定了蒙特卡洛射线追踪法可用于多种微藻物种和菌落构型，由于其复杂的几何形状，不均匀的性质以及与之相比的大尺寸，其吸收截面无法通过标准方法轻易地计算出来。入射光的波长。