Plant material
Individuals of both species were grown from seed in pots in a mix of Indiana Miami topsoil, ground pine bark and sand at a 0.5:1:0.5 ratio. Plants were between three and five years of age at the time of experiment. The plants were grown at Purdue University under controlled glasshouse conditions with approximately 12h natural light supplemented with LEDs (16h day, 8h night; Illumitex Power Harvest I4, TX, USA) providing a minimum photon flux at pot height of 150 μmol quanta m–2 s–1. Under well-watered conditions, plants received daily irrigation and complete liquid nutrients (Miracle-Gro® Water-Soluble All Purpose Plant Food, The Scotts Company LLC, OH, USA) once every month. Glasshouse temperatures were set at 28 °C during the day and 22 °C during the night. Air circulation fans in the glasshouse ensured continual air circulation, reducing boundary layer conductance.