Alfred-Wegener-Institut, Helmholtz-Zentrum für Polar- und Meeresforschung (AWI), 27570, Bremerhaven, Germany.
Institute of Biological Sciences, Applied Ecology and Phycology, University of Rostock, 18059, Rostock, Germany.
J Phycol. 2023 Jun;59(3):518-537. doi: 10.1111/jpy.13327. Epub 2023 Apr 10.
Coastal kelp forests produce substantial marine carbon due to high annual net primary production (NPP) rates, but upscaling of NPP estimates over time and space remains difficult. We investigated the impact of variable underwater photosynthetically active radiation (PAR) and photosynthetic parameters on photosynthetic oxygen production of Laminaria hyperborea, the dominant NE-Atlantic kelp species, throughout summer 2014. Collection depth of kelp had no effect on chlorophyll a content, pointing to a high photoacclimation potential of L. hyperborea towards incident light. However, chlorophyll a and photosynthesis versus irradiance parameters differed significantly along the blade gradient when normalized to fresh mass, potentially introducing large uncertainties in NPP upscaling to whole thalli. Therefore, we recommend a normalization to kelp tissue area, which is stable over the blade gradient. Continuous PAR measurements revealed a highly variable underwater light climate at our study site (Helgoland, North Sea) in summer 2014, reflected by PAR attenuation coefficients (K ) between 0.28 and 0.87 m . Our data highlight the importance of continuous underwater light measurements or representative average values using a weighted K to account for large PAR variability in NPP calculations. Strong winds in August increased turbidity, resulting in a negative carbon balance at depths >3-4 m over several weeks, considerably impacting kelp productivity. Estimated daily summer NPP over all four depths was 1.48 ± 0.97 g C · m seafloor · d for the Helgolandic kelp forest, which is in the range of other kelp forests along European coastlines.
滨海大型海藻林由于具有较高的年净初级生产力（NPP），因此会产生大量的海洋碳，但长时间和大范围内的 NPP 估算仍然很困难。我们研究了可变的水下光合有效辐射（PAR）和光合参数对 2014 年夏季主导北大西洋大型褐藻种——巨藻（Laminaria hyperborea）光合作用产氧量的影响。大型褐藻的采集深度对叶绿素 a 含量没有影响，表明巨藻对入射光具有很高的光适应潜力。然而，当用鲜质量归一化时，叶片梯度上的叶绿素 a 和光合作用与辐照度参数有显著差异，这可能会给整个藻体的 NPP 估算带来很大的不确定性。因此，我们建议对组织面积进行归一化，这在叶片梯度上是稳定的。连续的 PAR 测量显示，2014 年夏季我们研究地点（北海的赫尔戈兰岛）的水下光气候变化很大，PAR 衰减系数（K ）在 0.28 和 0.87 m 之间。我们的数据强调了连续水下光照测量或使用加权 K 值代表代表性平均值的重要性，以便在 NPP 计算中考虑到较大的 PAR 变异性。8 月的强风增加了浊度，导致在 3-4 m 以上的深度数周内出现负碳平衡，这对大型褐藻的生产力产生了重大影响。对所有四个深度的夏季每日 NPP 的估计值为 1.48 ± 0.97 g C·m 海底·d ，这一数值与欧洲沿海其他大型褐藻林的范围相当。
