Ayliffe L K, Cerling T E, Robinson T, West A G, Sponheimer M, Passey B H, Hammer J, Roeder B, Dearing M D, Ehleringer J R
Department of Geology and Geophysics, University of Utah, Salt Lake City, UT 84112, USA.
Oecologia. 2004 Mar;139(1):11-22. doi: 10.1007/s00442-003-1479-x. Epub 2004 Jan 17.
Temporal stable isotope records derived from animal tissues are increasingly studied to determine dietary and climatic histories. Despite this, the turnover times governing rates of isotope equilibration in specific tissues following a dietary isotope change are poorly known. The dietary isotope changes recorded in the hair and blood bicarbonate of two adult horses in this study are found to be successfully described by a model having three exponential isotope pools. For horse tail hair, the carbon isotope response observed following a dietary change from a C3 to a C4 grass was consistent with a pool having a very fast turnover rate ( t1/2 approximately 0.5 days) that made up approximately 41% of the isotope signal, a pool with an intermediate turnover rate ( t1/2 approximately 4 days) that comprised approximately 15% of the isotope signal, and a pool with very slow turnover rate ( t1/2 approximately 140 days) that made up approximately 44% of the total isotope signal. The carbon isotope signature of horse blood bicarbonate, in contrast, had a different isotopic composition, with approximately 67% of the isotope signal coming from a fast turnover pool ( t1/2 0.2 days), approximately 17% from a pool with an intermediate turnover rate ( t1/2 approximately 3 days) and approximately 16% from a pool with a slow turnover rate ( t1/2 approximately 50 days). The constituent isotope pools probably correspond to one exogenous and two endogenous sources. The exogenous source equates to our fast turnover pool, and the pools with intermediate and slow turnover rates are thought to derive from the turnover of metabolically active tissues and relatively inactive tissues within the body, respectively. It seems that a greater proportion of the amino acids available for hair synthesis come from endogenous sources compared to the compounds undergoing cellular catabolism in the body. Consequently, the isotope composition of blood bicarbonate appears to be much more responsive to dietary isotope changes, whereas the amino acids in the blood exhibit considerable isotopic inertia.
越来越多的研究通过动物组织中的时间稳定同位素记录来确定饮食和气候历史。尽管如此，饮食同位素变化后特定组织中同位素平衡速率的周转时间仍知之甚少。本研究中，通过一个具有三个指数同位素库的模型成功描述了两匹成年马毛发和血液碳酸氢盐中记录的饮食同位素变化。对于马尾毛，饮食从C3草变为C4草后观察到的碳同位素响应与一个周转速率非常快（半衰期约0.5天）的库一致，该库约占同位素信号的41%；一个周转速率中等（半衰期约4天）的库，约占同位素信号的15%；一个周转速率非常慢（半衰期约140天）的库，约占总同位素信号的44%。相比之下，马血液碳酸氢盐的碳同位素特征具有不同的同位素组成，约67%的同位素信号来自快速周转库（半衰期0.2天），约17%来自周转速率中等的库（半衰期约3天），约16%来自周转速率慢的库（半衰期约50天）。组成同位素库可能对应一个外源和两个内源。外源等同于我们的快速周转库，周转速率中等和慢的库分别被认为来自体内代谢活跃组织和相对不活跃组织的周转。与体内进行细胞分解代谢的化合物相比，似乎用于毛发合成的氨基酸中更大比例来自内源。因此，血液碳酸氢盐的同位素组成似乎对饮食同位素变化更敏感，而血液中的氨基酸表现出相当大的同位素惰性。
