Photosynthesis versus irradiance curves of Laminaria hyperborea off the island of Helgoland in summer 2014

Laminaria hyperborea off the island of Helgoland (North Sea, Germany) was sampled along a depth gradient (0.5, 2, 4, 6 m) throughout summer 2014. Discs were cut from three different blade regions (5, 25 and 50 cm above the stipe-blade transition zone) and set into photosynthesis versus irradiance (PI) curves. Incident light was generated by a slide projector (Liesegang Dianfant, Leitz Prado, Germany) equipped with a halogen lamp (Osram Xenophot 400 W/36 V, Germany) and 11 Schott neutral gray filters. Eleven light steps were conducted between 0 and 560 µmol photons m-2 s-1. Dark respiration was measured first for 20 mins followed by increasing light steps in 10 min intervals. Oxygen concentration expressed in % air saturation was logged by the OxyView software (Presens, Regensburg, Germany) and corrected for air pressure, salinity and logged temperature according to Tengberg et al. (2006). During post-processing, the oxygen production rate for each photon flux density (PFD) level was calculated by plotting a linear regression model through all O2-values measured during the time interval, and was normalized to either fresh mass (FM, unit: µmol O2 g–1 h–1) or disc surface area (DA, unit: µmol O2 cm–2 h–1).

本研究于2014年夏季在德国北海黑尔戈兰岛周边海域，沿0.5、2、4、6米的深度梯度对长海带（Laminaria hyperborea）开展采样。从藻柄-叶片过渡带上方5、25和50厘米处的三个不同叶片区域切取圆盘试样，用于光合-光强（photosynthesis versus irradiance，PI）曲线实验。入射光源由搭载德国产欧司朗Xenophot 400 W/36 V卤钨灯及11片肖特（Schott）中性灰度滤光片的幻灯机（德国Liesegang Dianfant、Leitz Prado型号）提供，实验设置了0至560 μmol光子·m⁻²·s⁻¹范围内的11个光强梯度。实验首先进行20分钟的暗呼吸速率测定，随后以10分钟为间隔依次提升光强开展后续测量。以空气饱和度百分比表示的氧浓度数据由德国雷根斯堡市普雷森斯（Presens）公司的OxyView软件记录，并依据Tengberg等人（2006）的研究方法，针对大气压强、盐度及实测水温进行校正。在后处理阶段，通过对单次测量时间区间内获取的全部氧气浓度数据进行线性回归拟合，计算得到每个光量子通量密度（photon flux density, PFD）水平下的产氧速率；随后将产氧速率分别以鲜重（fresh mass, FM，单位：μmol O₂·g⁻¹·h⁻¹）和圆盘试样表面积（disc surface area, DA，单位：μmol O₂·cm⁻²·h⁻¹）进行归一化处理。