Hofmann Laurie C, Heiden Jasmin, Bischof Kai, Teichberg Mirta
Marine Botany Department, Bremen Marine Ecology Center for Research and Education, University of Bremen, Leobener Straße NW2, 28359, Bremen, Germany,
Planta. 2014 Jan;239(1):231-42. doi: 10.1007/s00425-013-1982-1. Epub 2013 Oct 26.
Atmospheric carbon dioxide emissions cause a decrease in the pH and aragonite saturation state of surface ocean water. As a result, calcifying organisms are expected to suffer under future ocean conditions, but their physiological responses may depend on their nutrient status. Because many coral reefs experience high inorganic nutrient loads or seasonal changes in nutrient availability, reef organisms in localized areas will have to cope with elevated carbon dioxide and changes in inorganic nutrients. Halimeda opuntia is a dominant calcifying primary producer on coral reefs that contributes to coral reef accretion. Therefore, we investigated the carbon and nutrient balance of H. opuntia exposed to elevated carbon dioxide and inorganic nutrients. We measured tissue nitrogen, phosphorus and carbon content as well as the activity of enzymes involved in inorganic carbon uptake and nitrogen assimilation (external carbonic anhydrase and nitrate reductase, respectively). Inorganic carbon content was lower in algae exposed to high CO₂, but calcification rates were not significantly affected by CO₂ or inorganic nutrients. Organic carbon was positively correlated to external carbonic anhydrase activity, while inorganic carbon showed the opposite correlation. Carbon dioxide had a significant effect on tissue nitrogen and organic carbon content, while inorganic nutrients affected tissue phosphorus and N:P ratios. Nitrate reductase activity was highest in algae grown under elevated CO₂ and inorganic nutrient conditions and lowest when phosphate was limiting. In general, we found that enzymatic responses were strongly influenced by nutrient availability, indicating its important role in dictating the local responses of the calcifying primary producer H. opuntia to ocean acidification.
大气中的二氧化碳排放导致表层海水的pH值下降和霰石饱和状态降低。因此，预计钙化生物在未来海洋条件下会受到影响，但其生理反应可能取决于它们的营养状况。由于许多珊瑚礁经历着高无机养分负荷或养分可利用性的季节性变化，局部地区的珊瑚礁生物将不得不应对二氧化碳升高和无机养分变化的情况。仙人掌藻是珊瑚礁上的一种占主导地位的钙化初级生产者，对珊瑚礁的堆积有贡献。因此，我们研究了暴露于升高的二氧化碳和无机养分条件下的仙人掌藻的碳和养分平衡。我们测量了组织中的氮、磷和碳含量以及参与无机碳吸收和氮同化的酶（分别为胞外碳酸酐酶和硝酸还原酶）的活性。暴露于高二氧化碳环境下的藻类中无机碳含量较低，但钙化率并未受到二氧化碳或无机养分的显著影响。有机碳与胞外碳酸酐酶活性呈正相关，而无机碳则呈现相反的相关性。二氧化碳对组织中的氮和有机碳含量有显著影响，而无机养分则影响组织中的磷和氮磷比。硝酸还原酶活性在二氧化碳和无机养分升高条件下生长的藻类中最高，而在磷酸盐受限的情况下最低。总体而言，我们发现酶促反应受到养分可利用性的强烈影响，这表明其在决定钙化初级生产者仙人掌藻对海洋酸化的局部反应中起着重要作用。
