Evaporative cooling pad attenuates osmotic stress in closed-loop irrigated greenhouse roses

Ecological and economic considerations motivate the use of closed-loop irrigation to grow greenhouse crops on artificial substrates, submitting plants to increased osmotic stress due to heightened solute concentration of the irrigation solution. High solute concentration of re-circulated irrigation water, measured as electrical conductivity (EC), lowered the transpiration rate of flowering rose stems measured by the heat pulse method. The operation of an evaporative cooling pad decreased the transpiration rate by diminishing the water vapor deficit of the air in the greenhouse and slowed the rate of solute accumulation. Weaker evaporative demand also attenuated salinity induced decrease of transpiration rate. Leaf water potential and stomatal conductance corroborated that the wet-pad and fan alleviated osmotic stress caused by high concentration of the re-circulated irrigation solution.