2018 ASHS Annual Conference

±1^oC using a new galvanic cell oxygen sensor. Seedlings were grown at the same time in a ‘288 plug trays’ (individual cell volume = 40 cm³) in a soilless media until plants unfolded 3-10 leaves (species specific). Thirty root masses (including media) from each species were harvested (separated from the stem) and five masses were placed in each of six sealed (metal top) glass jars (240 cm³ volume) with an oxygen sensor mounted vertically through the top of each jar. A separate sensor was mounted in a jar with five media-only masses (taken from empty cells adjacent to plants) to quantify potential background microbial respiration in each cell. After closing jars, and a 1 hr stabilization period, absolute oxygen concentration was measured for two additional hours (data collected every 10 sec) and root respiration rate was calculated from a linear regression fit to kPa oxygen depletion over time. Respiration rate was calculated on a root fresh and dry mass (after washing media from roots) for each jar (5 masses). Respiration rate varied from -0.0000239 to -0.0000126 kPa 10 sec^-1 per gram fresh weight for Angelonia and Coleus, respectively. Respiration rate varied from to -0.000340 to -0.000184 kPa 10 sec^-1 per gram dry weight for Petunia and Tagetes, respectively.