Effects of Low Substrate Oxygen on Plant Growth

Oxygen in the rhizosphere is necessary for root respiration and, consequently, root growth and development.  Our objective was to determine the impact of irrigation practices on oxygen concentration in substrates.  In an initial study, marigold seedlings were grown in propagation trays under mist without drainage.  The volumetric water content (VWC) and oxygen concentration of substrates was monitored using sensors connected to a datalogger.  VWC of substrates increased throughout the course of the experiment and ranged from 0.26 to 0.75 L·L^-1 as the non-draining trays filled with water.  The oxygen concentration was between 21 and 18 kPa as substrate water content increased from 0.26 to 0.65 L·L^-1, but dropped to 5 kPa as the substrate water content increased to 0.75 L·L^-1.  In a second experiment, bedding plant seedlings were transplanted into six-inch pots with drainage or without drainage (i.e. placed on plastic saucers), and plants were hand watered daily.  The goal of this experiment was to quantify the impact of substrate water content on substrate oxygen concentration and to determine how low substrate oxygen concentration impacts shoot physiology, as indicated by stomatal conductance.