I am trying to model nutrient uptake and turnover from a long-term experiment. Currently I found a reference to a turnover rate for N used in Burton and Liken's classic study; however, when I asked the authors for the source of their estimate they (1) could not recall, and (2) did not provide a reference in the original paper.
Hey John...we labeled A. opacum larvae with 15N in two different treatment groups (single dose vs. two half-doses). We modeled the biological elimination rate of 15N post-metamorphosis (i.e., BER, the loss rate of δ15N) as an exponential decay using a non-linear regression model (PROC NLIN, SAS 2011). The exponential rate of elimination of 15N in the spiked treatments is due to both growth (i.e., new tissue) and metabolic tissue replacement (Hesslein, Hallard, and Ramlal 1993). We determined growth rate (k) of the newly metamorphosed salamanders using an exponential model (PROC NLIN, SAS 2011), and estimated metabolic turnover (m) as the difference BER – k = m. The BER of 15N averaged -0.2788 ± 0.0279 month-1 in the 15N-spike treatments. Post-metamorphic growth rates (k) did not differ among the treatment groups: control (0.154 ± 0.006 g month-1), single dose (0.139 ± 0.003 g month-1), and two dose (0.121 ± 0.015 g month-1). However, decreases over time in δ15N due to metabolic turnover (m) was faster (χ2 = 3.86, df = 1, P < 0.05) in the single-dose (-0.1812 ± 0.0080 month-1) compared to the two-dose treatment (-0.0790 ± 0.0203 month-1). Don't know if this will help you for N turnover rates but maybe. Cheers, --David
These folks just published some useful results.
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hi
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Dear all,
I am sorry to answer to your question with another question, but I think that you all could actually give me a very good and practical advice here.
Using 13C and 15N, I want to assess changes in diet composition in tadpoles and newt larvae after being exposed to a source of pollutant (with theoretically no direct effect on the consumers). The hypothesis is that the pollutant would affect the density of the sources (not the signature).
My questions are:
-Can we in this case, collect prey and consumers at the same time without really considering tissue turnover of the tadpoles and newt larvae?
-How much would you wait from the application of the pollutant in the water before collecting the animals (considering that in my situation, after max 4 weeks from the application, they will probably develop in adults).
-On the other hand, if you would collect sources and consumers with a delay, how much time would you expected to be necessary between the source and the consumer sampling?
Thank you all, and sorry again for invading your question.
Best regards
Alessandro Manfrin
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