Phycosphere pH of unicellular nano- and micro- phytoplankton cells and consequences for iron speciation.
Phycosphere pH of unicellular nano- and micro- phytoplankton cells and consequences for iron speciation.
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DOI：
10.1038/s41396-022-01280-1
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发表时间：
2022-10
期刊：
影响因子：
11
通讯作者：
Korchev, Yuri
中科院分区：
文献类型：
--
作者：
Liu, Fengjie;Gledhill, Martha;Tan, Qiao-Guo;Zhu, Kechen;Zhang, Qiong;Salaun, Pascal;Tagliabue, Alessandro;Zhang, Yanjun;Weiss, Dominik;Achterberg, Eric P.;Korchev, Yuri
由于人为的大气CO2吸收，表层海洋pH值正在下降，到2100年全球可能下降~0.3。细胞外pH值影响一系列生物过程，包括营养吸收、钙化和硅化。然而，关于浮游植物细胞周围的细胞外微环境（藻圈）的pH值与散装海水的差异，目前还没有很好的限制。这增加了环境变化的生物影响的不确定性。此外，先前的建模工作表明，小细胞的藻球pH值接近散装海水，但这尚未得到实验验证。在140 μmol光子·m−2·s−1条件下，康氏衣藻（直径5µm）、赫氏Emiliania huxleyi（直径5µm）、辐射盘藻（直径50µm）和瓦勒氏衣藻（直径100µm）的藻球pH值分别比普通海水（pH值8.00）高0.11±0.07、0.20±0.09、0.41±0.04和0.15±0.20（平均±SD）。当体海水pH值从8.00降低到7.78时，瓦勒氏梭菌的pH边界层厚度从18±4µm增加到122±17µm。藻圈pH受光合作用和碳酸氢盐胞外酶转化调节，也受光照强度、海水pH和缓冲能力的影响。pH值的变化改变了藻圈中铁的形态，因此浮游植物的铁可利用性可能更好地由藻圈来预测，而不是大量海水。总的来说，藻圈化学条件的精确量化对于评估海洋浮游植物对持续的海洋酸化和表层海洋铁限制的敏感性至关重要。
Surface ocean pH is declining due to anthropogenic atmospheric CO2 uptake with a global decline of ~0.3 possible by 2100. Extracellular pH influences a range of biological processes, including nutrient uptake, calcification and silicification. However, there are poor constraints on how pH levels in the extracellular microenvironment surrounding phytoplankton cells (the phycosphere) differ from bulk seawater. This adds uncertainty to biological impacts of environmental change. Furthermore, previous modelling work suggests that phycosphere pH of small cells is close to bulk seawater, and this has not been experimentally verified. Here we observe under 140 μmol photons·m−2·s−1 the phycosphere pH of Chlamydomonas concordia (5 µm diameter), Emiliania huxleyi (5 µm), Coscinodiscus radiatus (50 µm) and C. wailesii (100 µm) are 0.11 ± 0.07, 0.20 ± 0.09, 0.41 ± 0.04 and 0.15 ± 0.20 (mean ± SD) higher than bulk seawater (pH 8.00), respectively. Thickness of the pH boundary layer of C. wailesii increases from 18 ± 4 to 122 ± 17 µm when bulk seawater pH decreases from 8.00 to 7.78. Phycosphere pH is regulated by photosynthesis and extracellular enzymatic transformation of bicarbonate, as well as being influenced by light intensity and seawater pH and buffering capacity. The pH change alters Fe speciation in the phycosphere, and hence Fe availability to phytoplankton is likely better predicted by the phycosphere, rather than bulk seawater. Overall, the precise quantification of chemical conditions in the phycosphere is crucial for assessing the sensitivity of marine phytoplankton to ongoing ocean acidification and Fe limitation in surface oceans.
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