Effect of photosynthetic light dosage on carbon isotope composition in the coral skeleton: Long‐term culture of Porites spp.
Effect of photosynthetic light dosage on carbon isotope composition in the coral skeleton: Long‐term culture of Porites spp.
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DOI：
10.1029/2007jg000431
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发表时间：
2008-06
影响因子：
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通讯作者：
T. Omata;A. Suzuki;Takanori Sato;K. Minoshima;Eriko Nomaru;A. Murakami;S. Murayama;H. Kawahata;T. Maruyama
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文献类型：
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作者：
T. Omata;A. Suzuki;Takanori Sato;K. Minoshima;Eriko Nomaru;A. Murakami;S. Murayama;H. Kawahata;T. Maruyama
[1]虽然珊瑚骨架的氧同位素比率被用来重建过去有关海水的信息，但碳同位素比率被认为是生理过程的替代，主要是光合作用和呼吸作用。然而，珊瑚骨架等生物碳酸盐中碳同位素的分馏仍不清楚。我们进行了Porites spp的长期培养实验。在25℃±0.6°C的不同光照条件下(光照强度为100、300或500μ−m-2 S−1；每日光照周期为10或12 h)，研究光合作用对骨骼碳同位素组成的贡献。珊瑚生长在沙子过滤的海水中，没有被喂养；因此，它们依靠共生藻类的光合作用生存。随着光合作用有效辐射日剂量的增加，年延伸率也随之增大。随着辐射剂量的增加，平均同位素组成发生移动，碳同位素组成(δ~(13)C)变重，氧同位素组成(δ~(18)O)变轻。骨骼δ18O的减少与骨骼生长速度的增加相吻合，表明了所谓的动力学同位素效应的影响。观察到的δ13C的增加应该受到动力学和代谢同位素效应的影响，后者反映了共生藻类光合作用导致的骨骼δ13C的浓缩。利用δ13C-δ18O平面上的向量方法，我们区分了动力学和代谢同位素对δ13C的影响。由代谢同位素效应计算的δ13C变化是光剂量依赖性的。与代谢同位素效应相关的δ13C分馏曲线与光合作用-辐照度曲线非常相似，表明光合作用活性对代谢同位素效应的直接贡献。相反，随着生长速率的增加，与动力学同位素效应相关的δ13C分馏逐渐增加。我们的实验证明，珊瑚骨骼中的动力学和代谢同位素效应被成功地区分开来。
[1] Whereas the oxygen isotope ratio of the coral skeleton is used for reconstruction of past information on seawater, the carbon isotope ratio is considered a proxy for physiological processes, principally photosynthesis and respiration. However, the fractionation of carbon isotopes in biogenic carbonate such as coral skeleton is still unclear. We conducted a long-term culture experiment of Porites spp. corals at different light dosages (light intensity, 100, 300, or 500 μmol m−2 s−1; daily light period, 10 or 12 h) at 25 ± 0.6°C to examine the contribution of photosynthetic activity to skeletal carbon isotope composition. Corals were grown in sand-filtered seawater and not fed; thus, they subsisted from photosynthesis of symbiotic algae. As the daily dose of photosynthetically active radiation increased, the rate of annual extension also increased. Mean isotope compositions shifted; the carbon isotope compositions (δ13C) became heavier and the oxygen isotope compositions (δ18O) became lighter at higher radiation dose. Skeletal δ18O decrease coincided with increasing skeletal growth rate, indicating the influence of so-called kinetic isotope effects. The observed δ13C increase should be subject to both kinetic and metabolic isotope effects, with the latter reflecting skeletal δ13C enrichment due to photosynthesis by symbiotic algae. Using a vector approach in the δ13C–δ18O plane, we discriminated between kinetic and metabolic isotope effects on δ13C. The calculated δ13C changes from metabolic isotope effects were light dose dependent. The δ13C fractionation curve related to metabolic isotope effects is very similar to the photosynthesis–irradiance curve, indicating the direct contribution of photosynthetic activity to metabolic isotope effects. In contrast, δ13C fractionation related to kinetic isotope effects gradually increased as the growth rate increased. Our experiment demonstrated that the kinetic and metabolic isotope effects in coral skeleton were successfully differentiated.