悬浮泥沙对蓝藻光合及细胞化学计量的影响

选取水华微囊藻Microcystis flos-aquae为实验材料，在含不同浓度的悬浮泥沙中培养，测定其光合特性和胞内营养元素含量.结果显示，除低浓度悬浮泥沙组外，水华微囊藻比生长速率和chla浓度均低于对照组，且随着时间的延长，含泥沙组水华微囊藻的光合活性F_v/F_m显著下降.水华微囊藻的最大放氧速率P_m和光饱和点I_k随着泥沙浓度的增加而减小，而暗呼吸速率R_d和光抑制作用β显著升高.此外，随着泥沙浓度的升高，水华微囊藻单位细胞C和P含量显著降低，而单位细胞N含量略微升高；由于胞内P含量变化较大，导致N/P比和C/P比显著升高，而C/chla比值随泥沙浓度的增加呈下降的趋势.由此可见，悬浮泥沙虽然因光衰减效应减少了水华微囊藻胞内C含量以及能量供给，但微囊藻通过调节自身生理机能和代谢策略，优先补给C和提高N的合成，节约P合成的能量，通过调节胞内C：N：P储存的优化分配，以适应含悬浮泥沙的外界环境维持生长.

Effects of suspended sediments on photosynthetic and stoichiometrictraits of cyanobacteria

Microcystisflos-aquae, a dominant species of cyanobacteria in eutrophic waters was selected and cultivated in lab-scale batch experimentto investigate intracellular resourceallocation and stoichiometryunder different levels of suspended sediments. With the increase of suspended sediments, it was observed that the growth rate of M. flos-aquae and cholorophyll a (chla) significantly decreased. Simultaneous decreases of photosynthetic activity, maximum photosynthetic oxygen evolution rateand saturating irradiance, together with the increases of respiration rates and inhabitation effect of light irradiance were apparent. In addition, there was slight increases in cellular N of M. flos-aquae with increasing concentration of sediments, whereas C and P accumulation demonstrated the opposite trends. These resulted in the increases of intracellular N/P and C/P with the increase of suspended sediments. The ratio of C/chla decreased with the increase of suspended sediments. These evidencessupported that although suspended sediment produced light attenuation in the culture,and reducedthe intracellular C content and energy supply,M. flos-aquae preferentially replenished C, increased N synthesis and saved the energy consumption of P synthesis by adjusting its own eco-physiological functions and metabolic strategies. The fact that the optimum cellular stoichiometry of M. flos-aquae in response to suspended sediments presented a good example to understand the adaptive strategies of M. flos-aquae in field.