Net CO2 exchange, dark respiration, light compensation points, and light acclimatization rates were determined for Brassaia actinophyIla Endl., Nephrolepis exaltata (L.) Schott ‘Bostoniensis’, and Epipremnum aureum (Linden & Andre) Bunt under 4 irradiation levels. These 3 species exhibited increased rates of net CO2 uptake and decreased rates of dark respiration at the lowest irradiances, indicating an increase in photosynthetic efficiency. They demonstrated a 1.4 to 5.0 fold reduction in light compensation points over a 7 week period of acclimatization. Brassaia actinophylla reached its minimum light compensation point in 5 weeks, Epipremnum aureum in 3 weeks, and Nephrolepsis exaltata ‘Bostoniensis’ never reached a fixed light compensation point.
This study was conducted to evaluate the growth, visual quality, and stress response of 17 species of bedding plants and Kentucky bluegrass (Poa pratensis L.) grown outdoors for 10 weeks during the summer of 2003 at three locations in Colorado. Plants were irrigated at 100% of the reference evapotranspiration (ET0) (amount required to maintain Kentucky bluegrass in an optimum condition) for 2 weeks followed by 8 weeks at five irrigation levels: 0%, 25%, 50%, 75%, and 100% ET0. Begonia carrieri Hort. `Vodka', Lobelia erinus L. `Cobalt Blue', and Viola ×wittrockiana Gams. `Crown Gold' grew well with a minimum of 50% or more ET0 based on Kentucky bluegrass. Impatiens walleriana Hook. fil. `Tempo White' grew well only with 100% ET0. Antirrhinum majus L. `Sonnet Yellow', Dianthus L. `First Love', Lobularia maritima (L.) Desv. `Carpet White', and Pelargonium ×hortorum L.H. Bailey performed well with 25% to 50% ET0. The species Catharanthus roseus (L.) G. Don `Peppermint Cooler', Rudbeckia hirta L. `Indian Summer', Senecio cineraria D.C. `Silver Dust', Tagetes erecta L. `Inca Yellow' and T. patula L. `Bonanza Gold', Zinnia angustifolia Kunth., and Salvia farinacea Benth. `Rhea Blue', which are adapted to midsummer heat and low water, performed well with 0% to 25% ET0. Species considered to be heat or drought tolerant—Petunia ×hybrida hort. ex. E. Vilm. `Merlin White' and Glandularia J.F. Gmel. `Imagination'—required little or no irrigation. The bedding plant species evaluated in this study that required 25% or less ET0 are well adapted for low-water landscape installations.
The purpose of this experiment was to examine the effects of various root-zone temperatures and pH on Impatiens ×hybrida, New Guinea impatiens `Celebration Orange.' Greenhouse growers need to be cognizant of the root-zone medium pH, as New Guinea impatiens are sensitive to nutrient toxicities at low pH. It is thought that limestone at low root-zone medium temperatures is not quickly activated, leading to toxicities. The objectives of this project were to determine: the effect of root-zone medium pH on foliar symptoms of iron and manganese toxicity; and the effective rates and grind size of limestone on root-zone medium pH. Various rates of limestone and different grind sizes were incorporated into a sphagnum peat moss-based medium at a range of temperatures. This experiment used a two-way thermogradient plate to maintain varying, but stable root-zone medium temperatures, ranging from 12 to 42 °C. Plant growth as well as root-zone medium pH was monitored. Changes in root-zone medium pH were monitored over time. Results indicated that the addition of moderate or high rates of limestone, 6 or 3 kg·m-3, provided stable root-zone media pH over the course of time. Both limestone grind sizes at 325 and 100–200 mesh provided satisfactory starting and ending pH values for healthy New Guinea impatiens growth, especially between the root-zone temperatures of 30 and 18 °C. Higher and lower temperature extremes inhibited root growth, resulting in lower quality plants.
Chrysanthemum, ‘#3 Indianapolis White’, subjected continuously to atmospheres containing 1-4 ppm ethylene failed to initiate and develop flower buds under short day conditions. The plants showed typical epinastic symptoms, shortening of internodes, thickening of stems and loss of apical dominance. The plants developed many short axillary shoots, each with a few small leaves. The top leaves on the plant became smaller and smaller and were less dissected than the controls. Subjecting plants alternatively to ethylene containing and normal atmospheres generally prevented flowering also, but occasionally crown budding occurred. Bioassay of endogenous auxins showed that these growth promoting substances were maintained at high levels in the ethylene treated plants, which may account for their failure to flower. In addition, ethylene also seemed to affect the polar auxin transport system of the plant.