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.