[Enviro-lunch] Enviro-Lunch (2/7): C and N isotope fractionation during soil organic matter decomposition

[Kyungjin Min]

[image: image.png]

Hello all,

Next Monday (2/7), Dr. Michael Philben from Hope College will present a
seminar.  Please join us via zoom between 12-1 pm.

https://ucmerced.zoom.us/j/175736103

*Title*: Rethinking carbon and nitrogen isotope fractionation during soil
organic matter decomposition

*Abstract*

The stable isotope ratios of C and N are potentially powerful tools for
tracking the turnover of both elements. The enrichment of the heavier
element (13C and 15N) with increasing depth is commonly observed in soil
profiles, which is often attributed to a small fractionation of C and N
isotopes during organic matter decomposition. In this talk I will present
two studies that challenge the hypothesis that decomposition fractionates
these isotopes, both focused on organic horizon soils from the Newfoundland
and Labrador Boreal Ecosystem Latitudinal Transect (NL-BELT). To test C
isotope fractionation, we measured the C isotope mass balance of these
soils in both field and laboratory experiments. Neither of the major C
fluxes (CO2 via soil respiration or leached DOC) were significantly
depleted in 13C and therefore cannot explain the enrichment of 13C with
depth in the soil profile. To test N isotope fractionation, we measured the N
isotope ratios of hydroxyproline, a plant biomarker that is not
resynthesized by microbes in the soil. While other amino acids became
enriched in 15N with decomposition, hydroxyproline did not, indicating a
lack of N isotope fractionation during organic N mineralization. These
results challenge our conventional interpretation of C and N isotope ratios
in soils, but present new opportunities to rethink the meaning of these
stable isotope signals.


[image: Philben Headshot_png.png]

*Bio*

Mike Philben received a BA from Northwestern University in Earth and
Planetary Science with a minor in Chemistry. He went on to complete his PhD
in the Marine Science Program at the University of South Carolina, using
the biochemical composition of organic matter to interpret how peatlands
responded to past episodes of climate change.

Mike completed two postdocs after receiving his PhD. The first was with Sue
Ziegler at Memorial University of Newfoundland examining boreal forest
carbon and nitrogen cycle responses to climate change along a latitudinal
gradient. The second was at Oak Ridge National Laboratory on the Next
Generation Ecosystem Experiments-Arctic, focused on incorporating
permafrost ecosystems into Earth system models. He is currently an
Assistant Professor at Hope College in Holland, Michigan in the Departments
of Geology/Environmental Science and Chemistry.

He is a native of Redding, CA and misses the Golden State dearly this time
of year. He enjoys spending time with his 9-month old daughter Lily and his
6-year old hound dog Watson.


Sincerely,

co-host: KJ Min & Manisha Dolui

faculty coordinator: Asmeret Asefaw Berhe


-----

Spring 2022 Enviro-lunch schedule

 [image: image.png]
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.ucmerced.edu/pipermail/enviro-lunch/attachments/20220201/49cc0314/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: Philben Headshot_png.png
Type: image/png
Size: 556069 bytes
Desc: not available
URL: <http://lists.ucmerced.edu/pipermail/enviro-lunch/attachments/20220201/49cc0314/attachment-0003.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image.png
Type: image/png
Size: 118758 bytes
Desc: not available
URL: <http://lists.ucmerced.edu/pipermail/enviro-lunch/attachments/20220201/49cc0314/attachment-0004.png>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image.png
Type: image/png
Size: 28381 bytes
Desc: not available
URL: <http://lists.ucmerced.edu/pipermail/enviro-lunch/attachments/20220201/49cc0314/attachment-0005.png>