The isotopic composition of respired carbon dioxide in scleractinian corals: Implications for cycling of organic carbon in corals
The isotopic composition of respired carbon dioxide in scleractinian corals: Implications for cycling of organic carbon in corals
复制标题
石珊瑚中呼吸二氧化碳的同位素组成：对珊瑚中有机碳循环的影响
DOI：
10.1016/j.gca.2004.09.004
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发表时间：
2005
影响因子：
5
通讯作者：
J. Southam
中科院分区：
文献类型：
--
作者：
P. Swart;A. Szmant;J. Porter;R. Dodge;Jennifer I. Tougas;J. Southam
虫口珊瑚骨骼中δ13C变异的起源仍然是一个有相当大争议的问题。特别是，呼吸的二氧化碳在控制骨骼最终的δ13C方面所起的作用尚不清楚。在这项研究中，在一年的时间里，大约以每月一次的间隔测量了毛状藻呼吸产生的二氧化碳的δ13C的时间变异性。在这些实验中，三只珊瑚在佛罗里达群岛糖蜜礁附近8米深的平台上密闭培养24小时，孵化水样每隔3小时分析一次溶解无机碳(δ二氧化碳)的Σ13C。在整个孵化过程中，在小室内连续测量O2浓度。我们的结果表明，在白天，由于光合作用固定C的分馏作用，培养水中δ-CO2的Σ-13C变得富含13C，而在晚上，δ-CO2的Σ-13C变得更负。呼吸性二氧化碳的δ13C的范围从晚春的−9‰到秋季的−17‰。较轻的数值比之前的工作人员报告的珊瑚组织和虫黄藻的数值要负得多。这种差异的一个解释可能是珊瑚呼吸了相当大比例的同位素负物质，如脂类，与组织的整体‰13C相比，已知这些物质的值最高可轻10δ。呼吸性二氧化碳δ13C的明显季节变化表明，珊瑚组织的δ13C或呼吸的有机物质的类型和/或数量也存在季节变化。在1995年至1997年期间，从附近珊瑚礁每月收集的珊瑚组织样本的δ13C也观察到了类似的时间模式和变化幅度。这些模式在时间上与珊瑚骨骼中测量的δ13C相似。我们还计算了外部环境中溶解的二氧化碳−与虫黄藻固定的光合作用产物之间的分馏系数的年平均值为1.0121(±0.003)。这个值与整个生物体的光合作用与呼吸作用的比率(P/R)呈负相关，并在夏季表现出最高的值。
The origin of δ13C variations within the skeletons of zooxanthellate scleractinian corals is still a matter of considerable debate. In particular, the role respired CO2plays in controlling the eventual δ13C of the skeleton remains unclear. In this study, the temporal variability of the δ13C of respired CO2produced by Montastraea faveolata has been measured at approximately monthly intervals over a 1-year period. In these experiments, three corals maintained on a platform at 8 m depth near Molasses Reef in the Florida Keys were incubated in closed chambers for 24-h periods and samples of the incubation water analyzed for the δ13C of the dissolved inorganic carbon (ΣCO2) at ∼3-h intervals. Throughout the incubation, the concentration of O2was measured continuously within the chamber. Our results show that during daylight, the δ13C of the ΣCO2in the incubation water becomes enriched in13C as a result of fractionation during the fixation of C by photosynthesis, whereas at night the δ13C of the ΣCO2becomes more negative. The δ13C of the respiratory CO2ranges from −9‰ in the late spring to values as low as −17‰ in the autumn. The lighter values are significantly more negative than those reported by previous workers for coral tissue and zooxanthellae. An explanation for this discrepancy may be that the corals respire a significant proportion of isotopically negative substances, such as lipids, which are known to have values up to 10‰ lighter compared to the bulk δ13C of the tissue. The clear seasonal cycle in the δ13C of the respiratory CO2suggests that there is also seasonal variability in either the δ13C of the coral tissue or the type and/or amount of organic material being respired. A similar temporal pattern and magnitude of change was observed in the δ13C of the coral tissue samples collected from a nearby reef at monthly intervals between 1995 and 1997. These patterns are similar in timing to the δ13C measured in the coral skeletons. We have also calculated an annual mean value for the fractionation factor between dissolved CO2−in the external environment and photosynthate fixed by the zooxanthellae of 1.0121 (±0.003). This value is inversely correlated with the ratio of photosynthesis to respiration (P/R) of the entire organism and shows the highest values during the summer months.