同位素富集-稀释法研究食性转变对鱼类不同组织N同位素转化率的影响

稳定同位素技术广泛地用于描绘生态系统中食物网的食物来源和营养级关系,但是消费者不同组织转化率的研究相对较少。通过锦鲤摄食人工添加15N蓝藻的食性转化实验,研究不同组织N同位素转化率的差异,探讨组织生长和代谢对同位素转化的相对贡献,为不同时间尺度的稳定同位素研究取样奠定基础。结果表明,通过42d的加富蓝藻饲喂,各组织的N稳定同位素发生显著变化。肝的δ15N为(19.3±1.4)‰,显著高于其它组织,其次为鱼鳍((15.6±1.0)‰)和血液((12.6±0.4)‰),肌肉的δ15N‰最低,为(9.9±0.7)‰。在随后的同位素稀释实验中,锦鲤的体重增加,相对生长速率为0.011d-1,鳍肉的转化率最快,达到11.4%/d,半衰期仅为6.1d,其次是血液和肝,肌肉的转化率最低,仅有3.8%/d,半衰期最长,为18.4d。代谢衰减指数c和-1不存在显著差异,表明锦鲤各组织的N同位素转化主要由组织生长引起。结论显示,同位素富集-稀释法可以有效评价鱼类食性转变对不同组织同位素转化的差异,鳍肉和血液同位素分析可以作为锦鲤食性转变快速追踪的手段。

Effect of diet switch on turnover rates of tissue nitrogen stable isotopes in fish based on the enrichment-dilution approach

Nitrogen stable isotopes are widely used in ecological studies to estimate trophic position and determine movement patterns,but turnover rates of isotopes in animal tissues remain poorly understood.Here,we report nitrogen isotope turnover rates in different tissues of golden carp(Cryprinus carpiod).Turnover rate was estimated from the dilution of a 15N label introduced into consumer tissues by feeding of 15N-enriched cyanobacteria.The δ15N values of the four tissues varied significantly after a 15N enrichment diet feeding.Liver((19.3±1.4)‰) was significantly enriched in 15N relative to fin((15.6±1.0)‰) and blood((12.6±0.4)‰) tissues,and muscle((9.9±0.7)‰) had the most depleted 15N.Muscle tissue had the slowest turnover rates(3.8%/d),with half-lives of approximately 18.4d following a return to a diet with no 15N-enriched cyanobacteria addition,while the shortest half-life value for δ15N was in fin tissue(6.1 d).The exponent of metabolic decay,c wasn′t significantly different from-1 for δ15N in all the tissues,demonstrating that growth accelerated the rate of isotopic change and caused tissue specific turnover rates.The results support that the enrichment-dilution approach can be properly used to assess the dietary shifts on isotopic turnover rate,and further show that fin and blood stable isotope analysis is a quick approach to track dietary switch in golden carp.