I’m happy to present an InfoGraphic on Carbon Cycle Tracers created by University of Arizona art students Melissa Yepiz and Luke Williams in Prof Karen Zimmerman’s course on infographics. Creating this infographic on complex scientific concepts was not an easy task, but Melissa and Luke did an incredible job. Through this collaboration they have provided me with an invaluable resource for sharing my research to a range of audiences (and in a much more aesthetically pleasing way than usual). I learned a lot in the process, including how to better explain my science and to get down to the fundamentals of the message I wanted to share. I was blown away by the talent in the UA art department!
Two trace gases (carbonyl sulfide and the oxygen isotopes of CO2) show promise to help disentangle carbon cycle processes, but their soil fluxes need additional characterization. As in leaves, we anticipate that carbonic anhydrase (CA) enzymes in soil microbes drive uptake of atmospheric COS by soils (COS + H2O -> CO2 + H2S) and exchange of the oxygen isotopic signature between atmospheric CO2 and water (CO2 + H2O <-> HCO3– + H+). We performed a soil survey to test whether soil microbial CA drive the soil fluxes of these two potential carbon cycle tracers. By measuring the microbial, chemical, and physical properties of a diverse set of soils, we set out to determine the best predictors of exchange of COS and 18O-CO2, and specifically whether the abundance or diversity of microbial CA was the top predictor.
With the help of a large number of colleagues*, we collected and processed 20 soil samples from sites around the United States (including Hawaii) and from two sites in Cambodia. These soils represented a range of biomes and land use, as a number of soils came from sites used for agriculture.
This was my first experience working with soils, and I had a fantastic time! Soils are the result of coevolving biotic and abiotic components, and the results can be incredibly diverse. This diversity is evident in the range soil color and texture (see photo above), and was mirrored in our physical and chemical measurements. With support from a DOE Joint Genome Institute Community Science Program, we will be characterizing the microbial communities and their carbonic anhydrase expression to test whether soil microbial CA are linked with the soil exchange of these potential carbon cycle tracers.
*Max Berkelhammer, Ken Bible, Sebastien Biraud, Kristin Boye, Nona Ciariello, Ingrid Coughlin, Ankur Desai, Pat Dowell, Evan Goldman, Tom Guilderson, Paul Hanson, Marco Keiluweit, Kehaulani Marshall, Amy Meredith, Jesse Miller, Bharat Rastogi, Ulli Seibt, Christian von Sperber, Chris Still, Wu Sun, Jonathan Thom, Mary Whelan, Peter Vitousek.
Our manuscript on the “Seasonal fluxes of carbonyl sulfide in a midlatitude forest” was just recently published in PNAS (document online). Lead author Róisín Commane and I met at Harvard Forest where she installed an Aerodyne Research Inc., laser spectrometer to study the seasonal behavior of carbonyl sulfide (interchangeably called OCS and COS by different groups). Of particular interest are the common pathways to both CO2 and OCS, for example both trace gases react with carbonic anhydrase enzymes in leaves. This commonality may provide a quantitative, independent measure of the photosynthetic pathway for carbon assimilation.
In this study, we find that vegetative uptake accounted for 72% of annual uptake of OCS, and nighttime uptake through stomata and soil uptake accounted for the remainder. Emissions of OCS from the forest canopy and soils were observed episodically at the forest, and by an unknown mechanism.
We find that OCS and CO2 are in certain cases affected by different processes, making their relationship variable. Thus, OCS cannot be used as a direct tracer of photosynthetic activity, but can probe various aspects of ecosystem activity, such as stomatal conductance, which will be useful for constraining aspects of carbon cycling models.