The Effect of Intermittent Misting and Adventitious Root Development on Leafy Stem Propagule Water, Osmotic, and Turgor Potential Values

Understanding how intermittent misting affects water (Ψ), osmotic (Ψ_s), and turgor potential (P) of leafy propagules is fundamental in improving propagation success rates observed by ornamental nursery and greenhouse producers. The objectives of this study were to determine those environmental and/or physiologic factor(s) that exert the greatest influence on leafy stem propagule Ψ, Ψ_s and P values during adventitious root development; determine how Ψ, Ψ_s, and P values of propagules are affected by adventitious root formation; and determine differences in stock plant and propagule Ψ, Ψ_s, and P values during the adventitious root development process. Environmental factors examined included photosynthetically active radiation (PAR) (mmol•m^-2•s^-1), daily light integral (DLI), daily maximum PAR, daily mean temperature and daily maximum temperature. Propagule Ψ values of monarda and podocarpus were consistently more negative than stock plant Ψ values, although the differences in stock plant and propagule Ψ values were not significant. At no measurement was there any difference between monarda propagule Ψ_s values and stock plant Ψ_s values. However, monarda propagule Ψ_s were less varied over time than stock plant Ψ_s, likely a result of consistent moisture provided to propagules while under mist. Podocarpus propagule Ψ_s values were consistently less negative than stock plant Ψ_s values with one measurement being different; again likely a result of consistent moisture provided under mist. Turgor potential values of monarda propagules were consistently lower than stock plant P values, yet no significant difference between monarda propagule P values and stock plant P values was found. Turgor potential values of podocarpus propagules were less variable than stock plant P values. During the course of this study three trends were observed: 1) A lack of fluctuation in propagule Ψ, Ψ_S, and P measurements that is likely due to intermittent misting. 2) Fluctuation in stock plant Ψ, Ψ_S, and P measurements that is likely due to irrigation frequency of stock plants. 3) A lack of significance between stock plant and propagule Ψ, Ψ_S and P measurements indicate a lack of water stress in propagules, demonstrating the importance of intermittent misting to maintaining Ψ, Ψ_S, and P in propagules. It is known that misting is required to maintain proper propagule water balance, this study in conjunction with photosynthesis measurements (Chapter 2) and carbon allocation measurements (Chapter 3) demonstrate definitively that misting is vitally important to maintaining photosynthesis in propagules by sustaining adequate Ψ, Ψ_S, and P in propagules.