Deep chlorophyll maxima (DCM) and metalimnetic oxygen maxima (MOM) are outstanding biogeochemical features of acidic pit lakes (APL). However, knowledge of the eukaryotic phototrophs responsible for their formation is limited. We aimed at linking the dynamics of phototrophic communities inhabiting meromictic APL in Spain with the formation of these characteristic layers. Firstly, the dynamics of DCM and MOM and their relation to physico-chemical parameters (photosynthetically active radiation (PAR), pH, dissolved ferric iron concentration, temperature), pigments and nutrient distribution is described; secondly, the phototrophic community composition is studied through a combination of microscopy, biomolecular and “omics” tools. Phototrophic communities of the studied APL show a low diversity dominated by green microalgae, specifically Coccomyxa sp., which have been successfully adapted to the chemically harsh conditions. DCM and MOM are usually non-coincident. DCM correspond to layers where phototrophs have higher chlorophyll content per cell to cope with extremely low PAR (<1 µmol m⁻² s⁻¹), but where photosynthetic oxygen production is limited. MOM correspond to shallower waters with more light, higher phytoplankton biomass and intense photosynthetic activity, which affects both oxygen concentration and water temperature. The main drivers of DCM formation in these APL are likely the need for nutrient uptake and photo-acclimation.

中文翻译：

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Coccomyxa sp. 的适应。极低的光照条件会导致酸性坑湖中的叶绿素和氧气含量增加。


深层叶绿素最大值（DCM）和金属金属氧最大值（MOM）是酸性坑湖（APL）突出的生物地球化学特征。然而，对负责其形成的真核光养生物的了解是有限的。我们的目的是将居住在西班牙 meromictic APL 的光养群落的动态与这些特征层的形成联系起来。首先，描述了DCM和MOM的动态及其与理化参数（光合有效辐射（PAR）、pH、溶解三价铁浓度、温度）、色素和养分分布的关系；其次，通过结合显微镜、生物分子和“组学”工具来研究光养群落组成。所研究的 APL 的光养群落表现出较低的多样性，以绿色微藻为主，特别是Coccomyxa sp.，它们已成功适应了恶劣的化学条件。 DCM 和 MOM 通常不重合。 DCM 对应于光养生物每个细胞具有较高叶绿素含量以应对极低 PAR (<1 id=85>-2 s ^-1 )，但光合产氧有限的层。 MOM 对应于较浅的水域，具有更多的光照、更高的浮游植物生物量和强烈的光合作用活动，这会影响氧气浓度和水温。这些 APL 中 DCM 形成的主要驱动因素可能是营养吸收和光适应的需要。