Photosynthesis and respiration cause distinct chemical microenvironments within cyanobacterial aggregates. Here, we used microsensors and a diffusion–reaction model to characterize gradients in carbonate chemistry and investigate how these are affected by ocean acidification in Baltic vs. Pacific aggregates (Nodularia and Dolichospermum vs. Trichodesmium). Microsensor measurements of O₂ and pH were performed under in situ and expected future pCO₂ levels on Nodularia and Dolichospermum aggregates collected in the Baltic Sea. Under in situ conditions, O₂ and pH levels within the aggregates covered ranges of 80–175% air saturation and 7.7–9.4 in dark and light, respectively. Carbon uptake in the light was predicted to reduce HCO₃⁻ by 100–150 μmol L⁻¹ and CO₂ by 3–6 μmol L⁻¹ in the aggregate center compared to outside, inducing strong CO₂ depletion (down to 0.5 μmol L⁻¹ CO₂ remaining in the center) even when assuming that HCO₃⁻ covered 80–90% of carbon uptake. Under ocean acidification conditions, enhanced CO₂ availability allowed for significantly lower activity of carbon concentrating mechanisms, including a reduction of the contribution of HCO₃⁻ to carbon uptake by up to a factor of 10. The magnification of proton gradients under elevated pCO₂ that was predicted based on a lower buffer capacity was observed in measurements despite a concurrent decrease in photosynthetic activity. In summary, we provide a quantitative image of the inorganic carbon environment in cyanobacterial aggregates under present-day and expected future conditions, considering both the individual and combined effects of the chemical and biological processes that shape these environments.

中文翻译：

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当前和未来 pCO2 水平下蓝藻聚集体微环境中的碳酸盐化学

光合作用和呼吸作用在蓝藻聚集体中产生不同的化学微环境。在这里，我们使用微传感器和扩散反应模型来表征碳酸盐化学中的梯度，并研究波罗的海与太平洋聚集体（ Nodularia和Dolichospermum与Trichodesmium）中海洋酸化如何影响这些梯度。O ₂和 pH 值的微传感器测量是在波罗的海收集的结节藻和 Dolichospermum 聚集体的原位和预期的未来p CO ₂水平下进行的。在原位条件下，O ₂聚集体内的 pH 值和 pH 值分别覆盖 80-175% 的空气饱和度和 7.7-9.4 的黑暗和光照范围。与外部相比，预计光照下的碳吸收会使聚集体中心的 HCO ₃ ^-减少 100-150  μ mol L ^-1和 CO ₂减少 3-6  μ mol L ^{-1 ，从而导致强烈的 CO} ₂消耗（低至 0.5  μ mol L ^-1 CO ₂保留在中心），即使假设 HCO ₃ ^-覆盖了 80-90% 的碳吸收。海洋酸化条件下，CO _2增强可用性允许显着降低碳浓缩机制的活性，包括将 HCO ₃ ^-对碳吸收的贡献减少多达 10 倍。在p CO ₂升高的情况下质子梯度的放大是基于较低缓冲液预测的尽管光合活性同时降低，但在测量中观察到了容量。总之，我们提供了在当前和预期未来条件下蓝藻聚集体中无机碳环境的定量图像，同时考虑了塑造这些环境的化学和生物过程的单独和综合影响。