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- Author or Editor: Jan M. Kossowski x
- HortScience x
Long- and short-term physiological responses of pak choi (Chinese cabbage, Brassica campestris cv. `Hypro') to elevated CO2 and light environments were evaluated in the series of growth chamber experiments. Plants were grown hydroponically (Nutrient Film Technique) at 25/18°C (day/night) temperature, a 16-h photoperiod, and at three CO2 levels (350, 700, 1400 ppm) and two light levels (200 and 400 μmol·m–2·s–1 PPFD). Relative to 350-ppm CO2 treatment, the final total plant dry mass in low light increased by 37% and 38% at 700 and 1400 ppm CO2, respectively. In high light the increase was 7% and 13% at 700 and 1400 ppm CO2, respectively. Light response curves showed a positive CO2 effect on light compensation point, a slight increase in quantum yield and increase in maximum Pn rates at elevated CO2. Carbon dioxide response curves (measured at saturating PPFD of 1600 μmol·m–2·s–1) showed no effect of growth light treatment on the CO2 compensation point, but a 20% to 30% higher maximum Pn rate at saturating CO2 in plants grown at the higher light level. Overall, the highest Pn rates and the highest plant dry mass at final harvest were found in plants grown at the 400 μmol·m–2·s–1 PPFD and 1400 ppm CO2. Relative beneficial CO2 effects, however, were the most pronounced in low light conditions.
Cauliflower grown in hot and dry summer conditions is susceptible to a Ca and water-related physiological disorder known as tipburn. The objective of this research was to investigate the effect of several cultural practices influencing plant water relations on cauliflower yield, stomatal conductance and tipburn occurrence. `Snow Crown' seed was sown in field seedbeds on 21 Apr 1992 and seedlings transplanted to the production field on 10 June 1992. The experimental design was a split-plot with 4 replications. Main factor treatments were: a hygroscopic polymer, AquaMend, applied at 33.6 kg/ha in bands and rototilled before transplanting, night misting of plants beginning at head formation, and night covering of plants with a plastic tent, and a non-treated control. Plants in sub-plots were irrigated to field capacity when soil matric potential (SMP) reached a minima of -20, -50, or -80 kPa. Occurrence and severity of tipburn was rated as well as stomatal conductance. Marketable yields without wrapper leaves were measured on 2 harvest dates. Neither tipburn nor stomatal conductance were significantly effected by treatment although stomatal conductance showed a tendency to increase with decreasing SMP values Decreasing SMP also significantly increased yields, which is consistent with the simultaneous increase in stomatal conductance, and probably associated with the excessive rainfall and frequent flooding in 1992. The use of Aquamend significantly increased yield and head weight as SMP decrease. Among the cultural practices. Aquamend produced the greatest and tents the lowest yields. The use of Aquamend shows potential for increasing yields and decreasing irrigation requirements in cauliflower production in sandy soils.
Tipburn is considered a major limiting factor to lettuce production in greenhouses and controlled environment agriculture facilities. Conditions which promote optimal growth also result in high levels of tipburn incidence. It has been reported that air flow directed at inner leaves of rapidly growing lettuce can prevent tipburn without a concurrent reduction of growth, assumedly due to increased transpiration with increased air movement over leaf surfaces.
Lettuce was grown in the greenhouse in nutrient film technique, with additional lighting providing total of 17 to 19 mol m-2 d-1 of PAR. Control plants developed tipburn 20 to 25 days after seeding. Plants with air supplied to inner leaves by a perforated plastic sleeve did not develop tipburn up to 35 days after seeding. Diurnal changes in physiological parameters were measured starting one week prior to harvest. Leaves of control plants had significantly higher stomatal conductance and transpiration than did those of air-supplied plants, although diurnal patterns of control and air-treated plants were similar. Air flow treatment had no significant effect on the rate of photosynthesis. However, air-supplied plants had a slightly lower percentage of dry matter than control plants. The apparent growth reduction resulting from the air flow treatment evidently reduced the demand for calcium.