Paper in Nature Communications: Three-source dual-isotope partitioning

I am excited to announce that my three-source, dual-isotope partitioning approach has been published at Nature Communications! The paper describes a new technique to separate one pool (e.g., total soil CO2 emissions) into its three different sources (e.g., roots, soil organic carbon, and added plant litter), but still just using two stable isotopes (e.g., 12C/13C or 14N/15N). I’ll leave the details for the paper, which is open-access, but, briefly, it hinges on adding a double-treatment, where the experimental designs are identical, except one component has a different isotopic signature in treatment A vs. treatment B. (The figure below illustrates this graphically). The R code for analysis is published with the paper, so I am hoping it will be easily accessible to people who will find it useful – I think it could be an extremely powerful tool to help advance our understanding of element cycling in systems with more than two components.

A little story behind the paper: this review process was actually a pretty great experience. All the reviewers offered constructive comments, and I really felt like the end manuscript was much stronger after going through several rounds of revisions. One funny thing about this paper is related to the fact that I came up with the method out of necessity: I needed to separate soil, biochar, and plant root-derived CO2 in my field trial, but conventional isotope partitioning couldn’t handle three sources, and I didn’t have access to the resources to partition them by adding a radioactive isotope or something like that. I remember the moment I figured it out, and excitedly scrawling it on the chalkboard in the nook at the end of the hall in Bradfield while showing my labmate. If I had just been trying to showcase a new method, I probably would not have designed a field trial – notoriously messy – to demonstrate it! In my case, though, I just needed the method in order to do the field trial, and finish my Ph.D.. Hence, I’ll be really excited to start applying this new method in my new lab, in order to answer complex and exciting questions about three-(or more!)-way interactions in biogeochemical systems at finer scales.

Shading corresponds to illustrative values representing the isotopic composition (in arbitrary units) of each end-member (A, B and C) or the combined isotopic composition for a given system. Dashed lines along a single combined isotopic composition represent possible partitioning solutions for the combined sources. (a) Given an isotopic composition (here, a shade of grey representing an isotope value of 59) for a two-source system (rectangle between A and B) there is only one solution (that is, 38% from A and 62% from B), but for the three-source system (triangle of A, B and C), there is a range of solutions, shown along the dashed red line, which does not allow the three sources to be conclusively quantified. (b) By designing a system with two treatments, where the third component is present in two different isotopic forms that are otherwise identical (two leftmost triangles, as indicated by different shades for C1and C2), the range of solutions (dashed lines) will intersect at one point, which allows the total emissions to be partitioned conclusively into three parts (intersection of dashed lines in right triangle, indicating 25% A, 25% B and 50% C.

Shading corresponds to illustrative values representing the isotopic composition (in arbitrary units) of each end-member (A, B and C) or the combined isotopic composition for a given system. Dashed lines along a single combined isotopic composition represent possible partitioning solutions for the combined sources. (a) Given an isotopic composition (here, a shade of grey representing an isotope value of 59) for a two-source system (rectangle between A and B) there is only one solution (that is, 38% from A and 62% from B), but for the three-source system (triangle of A, B and C), there is a range of solutions, shown along the dashed red line, which does not allow the three sources to be conclusively quantified. (b) By designing a system with two treatments, where the third component is present in two different isotopic forms that are otherwise identical (two leftmost triangles, as indicated by different shades for C1and C2), the range of solutions (dashed lines) will intersect at one point, which allows the total emissions to be partitioned conclusively into three parts (intersection of dashed lines in right triangle, indicating 25% A, 25% B and 50% C.

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