# 4.4b N: Trophic vs. Source

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&#x26;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;


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://taylor-lindsay.gitbook.io/tl-comps/4.-isotopes/4.4-csia/4.4b-n-trophic-vs.-source.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.