The 2012 ASHS Annual Conference

Root zone oxygen is essential for root respiration.  Rhizospheric oxygen concentration is largely determined by diffusion rates with the atmosphere and is affected by substrate moisture level, temperature, and physical properties, as well as respiration rates and atmospheric O₂concentrations.  Plants growing in suboptimal rhizospheric oxygen levels undergo anaerobic respiration, which generates toxic by-products.  Suboptimal oxygen levels can reduce yield and growth, and increase root rot susceptibility.

Non-permeable containers may limit gaseous diffusion.  Elevated CO₂ levels associated with global warming could further deplete rhizospheric oxygen levels.  Determining dissolved oxygen (DO) requirements for optimal container plant production is critical to understanding how agricultural systems will respond to elevated CO₂and increased temperatures.  The objectives of this research were to: 1) evaluate a commercial oxygenation system (Water D.O.G.™ Iron Hunter HD) (WD) for elevating DO levels in irrigation water and 2) conduct preliminary investigations into response of woody species to elevated DO level in irrigation water when grown in a heavy or light substrate.  The DO concentration for W.D.-treated water and the municipal, river-based water supply (control) was measured to establish a consistent increase in DO due to WD treatment.  Experiments with plants used a CRD in a 2 (substrate) x 2 (water treatment) factorial arrangement with 8 blocks.  Forsythia x intermedia and Cornus florida were potted into 1-gal containers with a heavy or light substrate, bulk density 0.53 and 0.16 g/cc, respectively.  Experiment duration was 83 and 56 days for Forsythia and Cornus, respectively. W.D. DO was 4.1 mg/L greater than the control throughout the experiment.  DO had no effect on Cornus or Forsythia height.  Forsythia in the light substrate had greater height than in the heavy substrate.  For both species, there was no effect due to water treatment on dry weights although Cornus in the heavy substrate had 60% greater root dry weight with DO-treated water.  Substrate did influence root growth.  Cornus root dry weight was greater in the light substrate.  Forsythiagrowing in the light substrate had greater shoot, root, and total dry weight than those in the heavy substrate. The Water D.O.G.™ consistently increased DO levels above the municipal water control.  Substrate influenced biomass for Cornus and Forsythia.  Future work will examine the effects of elevated DO in irrigation water on growth of multiple species over a longer production period, less extreme environmental conditions, and using a typical nursery water supply (well water) rather than municipal water source.