Biological stoichiometry of Daphnia growth:: An ecophysiological test of the growth rate hypothesis
Biological stoichiometry of Daphnia growth:: An ecophysiological test of the growth rate hypothesis
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DOI：
10.4319/lo.2004.49.3.0656
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发表时间：
2004-05-01
影响因子：
4.5
通讯作者：
Elser, JJ
中科院分区：
文献类型：
--
作者：
Acharya, K;Kyle, M;Elser, JJ
生长速率假说（GRH）提出，生物体C:P和N:P比值的变化反映了在不同生长速率下，与富含磷的核糖体RNA分配改变相关的磷含量变化。我们通过检测食物数量和化学计量质量（不同的碳:氮:磷[C:N:P]比值）对两种水蚤（盔形溞，蚤状溞）幼体生长和化学成分（C:N:P、RNA和DNA含量）的影响来验证生长速率假说。在磷限制实验中，给溞喂食高磷（C:P = 110 ± 7.3）、中磷（456 ± 20.7）和低磷（934 ± 23.6）的饱和及限制浓度食物（尖针杆藻）；在氮限制实验中，给蚤状溞喂食高氮（C:N = 6.31 ± 0.35）、中1和中2（分别为9.0 ± 0.42；15.0 ± 0.49）以及低氮（18.22 ± 0.56）的饱和浓度食物。在磷限制实验中，两种水蚤在富磷、高食物量条件下生长最快，在缺磷、低食物量条件下生长最慢，这表明食物质量和数量均有影响。水蚤身体的磷百分比、C:P、N:P以及RNA百分比与生长速率紧密相关，并且RNA占身体总磷的很大一部分（48.8%[±2.0%]）。这种强烈的三方（生长 - RNA - P）相关性支持了生长速率假说。在氮限制实验中，食物的C:N对水蚤生长有适度影响。虽然P和RNA之间有良好的线性相关性，但生长速率与RNA含量和P含量无关，这表明在生长受氮限制的情况下，生长、RNA和P含量的三方耦合被打破，但对于这些条件还需要更多数据。这些数据有助于明确生长速率假说成立的生理条件，并且可能有助于解释来自野外和实验室研究的浮游动物身体化学计量的变化。
The growth rate hypothesis (GRH) proposes that variation in organism C: P and N: P ratios reflects variation in P content associated with altered allocation to P-rich ribosomal RNA under different growth rates. We tested the GRH by examining the effects of food quantity and stoichiometric quality (differing carbon: nitrogen: phosphorus [C: N: PI ratios) on juvenile growth and chemical composition (C: N: P RNA, and DNA contents) of two species of Daphnia (D. galeata, D. pulicaria). Daphnia in P-limited experiments were fed saturating and limiting concentrations of food (Scenedesmus acutus) of high P (C: P = 110 +/- 7.3), medium P (456 +/- 20.7), and low P (934 +/- 23.6), and in an N-limited experiment D. pulicaria was fed saturating concentrations of high N (C: N = 6.31 +/- 0.35), medium 1 and medium 2 (9.0 +/- 0.42; 15.0 +/- 0.49, respectively), and low N (18.22 +/- 0.56) food. In P-limited experiments, both Daphnia species grew fastest under P-rich, high food conditions and grew slowest under P-deficient, low food conditions, showing effects of both food quality and quantity. Daphnia body percentage P, C: P, N: P and percentage RNA were tightly correlated with growth rates, and RNA contributed a significant fraction of total body P (48.8% [+/-2.0%]). This strong three-way (growth-RNA-P) set of correlations supports the GRH. In the N-limited experiment, food C: N had a moderate effect on Daphnia growth. While there was a good linear correlation between P and RNA, growth rate was uncorrelated with RNA content and P content, suggesting that the three-way coupling of growth, RNA, and P content is broken under N limitation of growth, but more data for these conditions are needed. These data help in delineating the physiological conditions under which the GRH holds and may be useful in interpreting variation in body stoichiometry of zooplankton from field and lab studies.