Paper accepted: Stable Isotope collaboration, Chris Bickford

Christopher P. Bickford, Nate G. Mcdowell, Erik Barry Erhardt, Heath H. Powers, David T. Hanson. (2009) “High frequency field measurements of diurnal carbon isotope discrimination and internal conductance in a semi-arid species, Juniperus monosperma“. Plant, Cell & Environment, online Volume 32, Issue 7, pages 796–810, July 2009. Chris Bickford, PhD candidate UNM Biology, and I met when we attended Iso-Camp at Jim Ehleringer’s lab at U Utah Summer 2008.  On the flight home we started discussing a challenge he was facing in his first of three dissertation papers. He studies details of plant photosynthesis.  He had complicated expressions for leaf carbon isotope discrimination $$\Delta$$ and internal conductance $$g_i$$ based on CO$$_2$$ concentrations of CO$$_2$$ isotopologues $$^{13}C^{16}O^{16}O$$ and $$^{12}C^{16}C^{16}O$$. He needed to propigate the variation of the CO$$_2$$ measurements into his variables of interest, $$\Delta$$ and $$g_i$$.  He also needed to compare his accurate and precise measurements using tunable diode laser spectroscopy (TDL) to predictions from three models. There were a number of statistical issues.  One was how to make model and observation comparisons.  I suggested using RMSE since it includes both variance and bias in the single measurement.  The main issue was the incorporation of variation from the CO$$_2$$ measurements into the quantities of interest.  The bootstrap allowed us to do this.  There were a number of programming sessions in R to write functions and scripts to do all the calculations, create plots, output spreadsheets of results, and so on.  Chris has become a convert from Excel to R over the course of this project.  These methods implemented on this paper will likely flow into later pubs for both Chris and Dave. Chris has taken a postdoc in New Zealand, where he and his wife, Karen, will spend the next two years with their dog.  He defends his dissertation on April 13th.

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