> For the complete documentation index, see [llms.txt](https://taylor-lindsay.gitbook.io/tl-comps/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://taylor-lindsay.gitbook.io/tl-comps/4.-isotopes/4.4-csia/4.4b-n-trophic-vs.-source.md).

# 4.4b N: Trophic vs. Source

16

Trophic amino acids 

* heavily fractionating
* glutamic acid
* commonly undergo transamination 

Source amino acids 

* minimally fractionating <mark style="color:red;">- not zero fractionation</mark>
* phenylalanine&#x20;
* commonly undergo hydroxylation&#x20;
* show the baseline&#x20;

<figure><img src="https://789240665-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FShvdx4K6BBMxfuVPr2NP%2Fuploads%2Fq8cnGYMdu24kGNB99eA5%2FDifference-Between-Transamination-and-Deamination-Tabular-Form.webp?alt=media&amp;token=22660f29-509e-4c26-994d-09d3abd9ce07" alt=""><figcaption></figcaption></figure>

Trophic position = trophic - source = Glu - Phe&#x20;

* same source with different trophic means variation in diet&#x20;
* same trophic position/difference between trophic & source means baseline variability&#x20;

TDF

* measured TDF glu-phe values are consistently lower than expected&#x20;
  * **diet quality** - amino acid imbalance with low diet quality leads to more de novo biosynthesis -> increased Glu transamination = higher TDF&#x20;
    * In carnivores: higher protein content = higher excretion rate = higher TDF&#x20;
    * In Herbivores: lower protein content = lower excretion rate = lower TDF&#x20;
  * **Waste type** - ammonia producers have higher TDFs than urea/uric acid producers&#x20;
  * This change can be included in trophic position models by using multiple TDFs as you move up the food chain&#x20;
* Basically the same things as TEF except for the rationale behind the word choice (Kelton prefers TEF)&#x20;

Beta&#x20;

* β = δ15NGlu - δ15NPhe in 1° producers
* vascularization drives beta values (not habitat or mode of photosynthesis)&#x20;
* Phe is the main precursor to many secondary compounds in plants, including lignin&#x20;
* non vascular plants have higher beta value than vascular&#x20;

Microbial N&#x20;

* Microbial N metabolism is highly complex&#x20;
* mixotrophic organisms&#x20;
* Microbes have a very low & highly variable TDF&#x20;

SumV

* degree of microbial working of organic matter&#x20;