The role of irradiance in controlling coralline algal calcification

Coralline algae are an essential element of benthic ecosystems throughout the ocean’s photic zone. Yet, the role of light in shaping the physiology of coralline algae from cold-water, low-light habitats is poorly understood. Here, we assess the calcification physiology of five cool-temperate coralline algae in response to different irradiances over three months. We show that in contrast to current models focused on warmer water species, previously observed enhancement of calcification rates by photosynthesis is largely limited to lower irradiances, and that the removal of CO2 from the calcifying fluid is not the underlying mechanism of this enhancement. Instead, this likely occurs via two processes: 1) increased ion pumping rates to elevate the calcium carbonate saturation state in the calcifying fluid; and 2) a higher daytime pH in the diffusion boundary layer that raises calcifying fluid pH. However, as irradiance increases, ion pumping becomes increasingly saturated limiting further ..., Chlorophyll flourometry was used to obtain Fv/Fm (variable fluorescence [Fv] normalised to maximal fluorescence [Fm]), rETRmax (maximum relative elctron transport rate), Ek (minimum saturation intensity) and alpha (light use efficiency). Skeletal magnesium content in mol% and Full-Width-Half-Maximum were measured using confocal Raman spectroscopy. Chlorophyll a, phycoerything and phycocyanin content was calculated from absorbance readings (UV-vis spectrophotometer). Calcification rates were calculated from changes in weight (buoyant weight) which were normalised for surface area (cm-2) and time (d-1). Short-term calcification rates in the dark and the light were calculated from changes in total alkalinity which were normalised for surface area (cm-2) and time (h-1). Photosynthetic rates (gross) were calculated from changes in oxygen (O2) during the day (net photosynthesis) and the night (dark respiration) which were normalised for surface area (cm-2) and time (h-1). Organic tissue carb...,珊瑚藻（Coralline algae）是全球海洋透光带底栖生态系统的核心组成部分。然而，针对冷水弱光生境下珊瑚藻的生理特征受光照调控的机制，当前学界认知仍较为匮乏。本研究针对5种温带冷水珊瑚藻开展为期3个月的实验，探究其钙化生理对不同光照强度的响应规律。研究结果显示，与现有针对暖水物种的模型结论相悖，此前观测到的光合作用对钙化速率的促进效应仅在较低光照强度下显著存在；且钙化液中CO₂的移除并非该促进效应的核心机制。取而代之的是，该效应可能通过两种途径实现：1）提升离子泵速率以提高钙化液内的碳酸钙饱和状态；2）提升扩散边界层日间pH值，进而升高钙化液pH。然而，随着光照强度升高，离子泵会逐渐达到饱和，进而限制进一步的…… 采用叶绿素荧光法测定相关参数：Fv/Fm（可变荧光Fv与最大荧光Fm的比值）、最大相对电子传递速率rETRmax、最小饱和光强Ek以及光能利用效率α。 利用共聚焦拉曼光谱法，测定了骨骼中以摩尔百分比计的镁元素含量以及半高宽（Full-Width-Half-Maximum, FWHM）。 通过紫外-可见分光光度计的吸光度读数，计算得到叶绿素a、藻红蛋白（phycoerythrin）与藻蓝蛋白（phycocyanin）的含量。 通过重量变化（悬浮重量法）计算钙化速率，并以表面积（单位：cm⁻²）和时间（单位：d⁻¹）进行标准化校正。 暗环境与光照条件下的短期钙化速率，则通过总碱度的变化计算得到，同样以表面积（单位：cm⁻²）和时间（单位：h⁻¹）进行标准化校正。 总光合速率通过日间（净光合作用）与夜间（暗呼吸作用）的氧气浓度变化计算得到，并以表面积（单位：cm⁻²）和时间（单位：h⁻¹）进行标准化校正。 有机组织碳……