Sofía Gómez
Major Professor: Dr. Celina Gómez
MS DEFENSE SEMINAR
October 2nd at 9:00 AM
HORT 222
“CHARACTERIZING ENVIRONMENTAL EFFECTS ON THE WATER STATUS OF CUTTINGS ACCLIMATED INDOORS”
Abstract: Vertical indoor propagation (VIP) systems that use sole-source lighting and temperature, relative humidity (RH), and carbon dioxide (CO2) control are increasingly being used by young-plant growers to start unrooted cuttings (URC) indoors for greenhouse finishing. However, optimal environmental setpoints for VIP systems are unknown. Managing factors to limit water loss by URC prior to root initiation is particularly critical for VIP systems to decrease crop losses and shorten rooting times. In chapter 1, we characterized the effect of blue light and CO₂ concentration on the water status of Chrysanthemum and Begonia cuttings, as both factors are known to affect stomatal regulation of plants. The first experiment evaluated short-term effects of blue light (15% to 60% blue light) on water-use and physiological responses by URC. This was followed by a second experiment that evaluated short-term effects on water use and long-term effects on evapotranspiration, physiological responses, and growth of cuttings under two blue-light treatments (21% or 45% blue light) and two CO2 concentrations (ambient or high at ~500 or 1200 μmol·mol–1, respectively). In the first experiment, increasing blue light increased short-term water use but did not affect stomatal conductance (gs) and transpiration (E), likely due to limitations in stomatal control by URC. Results from the second experiment showed there were few growth differences in response to blue light at the two CO2 concentrations, suggesting that growth of cuttings is more responsive to environmental stimuli after root initiation. When significant, growth responses were species-specific, likely attributed to morphological and anatomical differences. The only effect in long-term evapotranspiration was measured in begonia under high CO2, which indicated that cuttings under 45% blue light had the highest water loss. This result corresponds with the general findings for gs and E. In chapter 2, we evaluated the combined effect of photosynthetic photon flux density (PPFD) (0 to 210 μmol·m–2·s–1) and vapor pressure deficit of the air (VPDair) (0 to 0.76 kPa) on various environmental factors, and on the short-term water status of cuttings, as they are both major drivers of water loss. Results showed that PPFD had minimal heating effects, which suggests that measurements of leaf temperature are likely unnecessary in VIP systems where PPFD is typically low and environmental conditions are constant. In general, the water status of begonia was minimally affected by PPFD and VPDair, but that of chrysanthemum was responsive to both variables. For chrysanthemum URC, water loss and water uptake tended to increase in response to increasing PPFD, but there was no response to PPFD in gs, E, evapotranspiration, and relative water content (RWC). For rooted cuttings (RC), however, gs and E followed a linear increasing response to increasing PPFD, suggesting they were able to regulate transpirational losses through water uptake from the substrate. Increasing VPDair linearly increased the rate of water loss, water uptake, and evapotranspiration by chrysanthemum URC and RC, which in turn reduced RWC, whereas the leaf-air temperature difference linearly decreased in response to increasing VPDair, likely attributed to an increase in evaporative cooling under less saturated conditions. Overall, results from our studies provide baseline information on how different environmental conditions in VIP systems affect water use by cuttings from two ornamental herbaceous species.