A simple role of coral-algal symbiosis in coral calcification based on multiple geochemical tracers
A simple role of coral-algal symbiosis in coral calcification based on multiple geochemical tracers
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基于多种地球化学示踪剂的珊瑚-藻类共生在珊瑚钙化中的简单作用
DOI：
10.1016/j.gca.2018.05.016
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发表时间：
2018
影响因子：
5
通讯作者：
Gussone
中科院分区：
文献类型：
--
作者：
Nakamura;Tanaka;Shinzato;Suzuki;Yokoyama;Kawahata;Gussone
造礁珊瑚的光增强钙化，最终形成巨大的珊瑚礁，是众所周知的，基于珊瑚-藻类共生。关于共生体光合作用与珊瑚钙化之间的联系，人们提出了几个有争议的假说，包括池内pH值的升高、有机基质分泌的作用和酶活性。在此，基于共生和非共生原生珊瑚虫的骨骼化学和同位素组成，我们证明了钙化介质中简单的pH值增加是共生体对宿主珊瑚钙化的主要贡献。我们使用共生和非共生原生息肉，在四种温度（27、29、31和33 °C）、五种盐度（34、32、30、28和26）和四种pco2水平（<300、400、800和1000 µatm）下饲养10 天。通过对多种地球化学示踪剂（U/Ca、Mg/Ca、Sr/Ca、δ18O、δ13C和δ44Ca）的分析，发现骨骼U/Ca比值（作为钙化液pH值的代表）明显下降，表明共生息肉中钙化液的pH值高于非共生息肉。相比之下，共生和非共生息肉的Mg/Ca比率（用作有机基质分泌的临时代理）和δ44Ca（用作Ca2+途径的指示物）没有差异。这表明与珊瑚钙化相关的有机基质分泌主要由珊瑚宿主自身控制，Ca2+的跨膜转运不随共生关系而变化。共生和非共生珊瑚虫的骨骼δ18O值在温度依赖性相同的情况下均存在偏移。基于一个新提出的模型，本研究中δ18O的行为似乎反映了钙化流体中co2的水化速率。由于二氧化碳水合作用是由碳酸酐酶促进的，因此共生和非共生息肉之间δ18O值的差异归因于酶活性的差异，尽管该酶在非共生息肉中也有功能。温度和盐度实验中的共生δ13C值比光合作用下的共生δ13C值更高，尽管pco2实验中的光合δ13C信号被海水中溶解无机碳的δ13C梯度所掩盖，而δ13C梯度是由高pco2处理中13c耗尽的co2气体添加引起的。Sr/Ca比值与温度、盐度和二氧化碳分压的关系可以忽略不计，尽管这可能归因于本研究中Sr/Ca比值重复的较大偏差。总体而言，在所有实验中，只有共生和非共生珊瑚虫的U/Ca比值存在显著差异，说明共生藻类对珊瑚钙化的关键作用是光合作用使钙化液pH升高。
Light-enhanced calcification of reef-building corals, which eventually create vast coral reefs, is well known and based on coral-algal symbiosis. Several controversial hypotheses have been proposed as possible mechanisms for connecting symbiont photosynthesis and coral calcification, including pH rise in the internal pool, role of organic matrix secretion, and enzyme activities. Here, based on the skeletal chemical and isotopic compositions of symbiotic and asymbiotic primary polyps ofAcropora digitiferacorals, we show a simple pH increase in the calcification medium as the predominant contribution of symbionts to calcification of host corals. We used the symbiotic and asymbiotic primary polyps reared for 10 days at four temperatures (27, 29, 31, and 33 °C), five salinities (34, 32, 30, 28, and 26), and four pCO2levels (<300, 400, 800, and 1000 µatm). As a result of analyzing multiple geochemical tracers (U/Ca, Mg/Ca, Sr/Ca, δ18O, δ13C, and δ44Ca), a clear and systematic decrease in skeletal U/Ca ratio (used as a proxy for calcification fluid pH) was observed, indicating a higher pH of the fluid in symbiotic compared to asymbiotic polyps. In contrast, Mg/Ca ratios (used as a tentative proxy for organic matrix secretion) and δ44Ca (used as an indicator of Ca2+pathway to the fluid) did not differ between symbiotic and asymbiotic polyps. This suggests that organic matrix secretion related to coral calcification is controlled mainly by the coral host itself, and a transmembrane transport of Ca2+does not vary according to symbiosis relationship. Skeletal δ18O values of both symbiotic and asymbiotic polyps showed offsets between them with identical temperature dependence. Based on a newly proposed model, behavior of δ18O in the present study seems to reflect the rate of CO2hydration in the calcifying fluid. Since CO2hydration is promoted by enzyme carbonic anhydrase, the offset of δ18O values between symbiotic and asymbiotic polyps is attributed to the differences of enzyme activity, although the enzyme is functional even in the asymbiotic polyp. Symbiotic δ13C values in the temperature and salinity experiments were higher compared to those in the asymbiotic polyps due to photosynthesis, although photosynthetic δ13C signals in the pCO2experiment were masked by the dominant δ13C gradient in dissolved inorganic carbon in seawater caused by13C-depletd CO2gas addition in the higher pCO2treatments. Sr/Ca ratios showed a negligible relationship according to variation of temperature, salinity, and pCO2, although it might be attributed to relatively large deviations of replicates of Sr/Ca ratios in the present study. Overall, only the U/Ca ratio showed a significant difference between symbiotic and asymbiotic polyps throughout all experiments, indicating that the critical effect on coral calcification caused by symbiotic algae is the increase of pH of the calcifying fluid by photosynthesis.
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影响因子：
2.8
作者：
Hopkinson, Brian M.;Tansik, Anna L.;Fitt, William K.
通讯作者：
Fitt, William K.
影响因子：
5
作者：
T. Omata;A. Suzuki;H. Kawahat;M. Okamoto
通讯作者：
T. Omata;A. Suzuki;H. Kawahat;M. Okamoto
影响因子：
5
作者：
M. Inoue;N. Gussone;Y. Koga;A. Iwase;A. Suzuki;K. Sakai;H. Kawahata
通讯作者：
M. Inoue;N. Gussone;Y. Koga;A. Iwase;A. Suzuki;K. Sakai;H. Kawahata
影响因子：
5
作者：
Grottoli, AG
通讯作者：
Grottoli, AG
海水pH值对石珊瑚冷水珊瑚Lophelia pertusa U/Ca比值的影响
影响因子：
4.9
作者：
Raddatz;Rüggeberg;Flögel;Hathorne;Liebetrau;Eisenhauer;W.-Chr.
通讯作者：
W.-Chr.