Supplement 1. Data used in the present analysis, including new stomatal slope data for five species and previously published Switchgrass observations of Vc,max, SLA, leaf width, and fine-root : leaf ratio.

File List stomatal_slope.csv (MD5: e7be44c77a35e03b1f4b8d3666f7ebb1) pavi_data.csv (MD5: 614c310d746cb8f31a58db3a8c7a23e9) – Previously published Switchgrass data used in the present analysis. Description Stomatal slope was estimated using measurements of four leaves from each of five field-grown energy crop species during the 2010 growing season. The five species included two C4 grasses: Miscanthus (<i>Miscanthus x giganteus</i>) and Switchgrass (<i>Panicum virgatum</i>) planted in 2008 and three deciduous tree species: Red Maple (<i>Acer rubrum</i>), Eastern Cottonwood (<i>Populus deltoides</i>) and Sherburne Willow (<i>Salix x Sherburne</i>) planted in 2010 as 2 year old saplings. All plants were grown at the Energy Biosciences Institute Energy Farm (40°10'N, 88°03'W). Photosynthesis (A), stomatal conductance (gs), intercellular [CO₂] (ci), and humidity deficit at the leaf surface (Ds) were obtained via open gas exchange systems with 2 cm² leaf chambers housing infrared gas analyzers to measure fluxes of both CO₂ and water (LI-6400; LI-COR Inc., Lincoln, NE, USA). Data were collected following a simplified version of the protocol described by Leakey et al. (2006) in which photosynthetic photon flux density was maintained at 1500 μmol·m^-2·s^-1, leaf temperature was 25±3°C and the vapor pressure deficit from leaf to air was &lt; 2 kPa while [CO₂] entering the chamber was varied stepwise (400, 250, 350, 450, 650, 850, 1200, 1500 ppm). A minimum of 20 minutes was allowed for A and gs to completely stabilize before data were collected at each [CO₂]. For each individual leaf, linear least squares regression was used to estimate the stomatal slope based on the Ball et al. (1987) model of stomatal conductance (not used in present study but provided as data in <b>[appendix]</b>), and then separately for the Leuning (1995) model of stomatal conductance. A common value of Γ = 40μP/Pa, and D₀ = 1500 Pa was used in accordance with Leuning (1995). The stomatal_slope.csv file contains the following columns: number: order of measurement species: latin name of plant species measured m_bb: slope from the Ball et al. (1985) model se_bb: standard error for estimate of m_bb m_leuning: slope from Leuning (1995) model m_se_leuning: standard error for estimate of m_leuning go_leuning go_se_leuning: standard error for estimate of go_leuning trait_id: primary key for identification in BETYdb (www.betydb.org), additional metadata available for trait <i> available at www.betydb.org/traits/<i> </i></i><i><i> </i></i><i><i> </i></i> The pavi_data.csv file contains the following columns: trait: name of trait, with units mean: mean of observations n: number of observations se: standard error (or conservative estimate of standard error, derived using calculations in <b>[Supplement 2</b>]). citation: Author and year citation where first published (see below) trait_id: primary key for identification in BETYdb (www.betydb.org), additional metadata available for trait <i> available at www.betydb.org/traits/&gt; </i><i> </i><i> </i><i><i><i> </i></i></i>