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Qingwu Meng, Jennifer Boldt, and Erik S. Runkle

the ratio of R to FR radiation, can evoke the shade-avoidance response to modify morphological traits ( Franklin, 2008 ). A typical green leaf of plants grown in growth chambers absorbed ≈92% of B radiation (450 nm), 92% of R radiation (660 nm), and 81

Open access

Andrea Stuemky and Mark E. Uchanski

cultivars of strawberry only flower and bear fruit during specific times of the year as a result of corresponding daylength. This phenomenon is referred to as the photoperiod response. However, certain strawberry cultivars produce flowers and fruit

Free access

Qibing Wang and Jianjun Chen*

Ficus benjamina is considered to have a high degree of morphological and physiological plasticity in response to light levels. In this study, leaf area and thickness, specific leaf area (SLA), chlorophyll content, and photosynthetic characteristics of Ficus benjamina `Common'; grown in a shaded greenhouse under four maximum photosynthetic photon flux densities (PPFDs) of 150, 250, 450, or 650 μmol·m-2·s-1 were investigated. Results showed that plants grown under 450 and 650 PPFDs had higher SLA and leaf thickness but smaller leaf areas than those grown under 150 and 250 PPFDs. Total chlorophyll content per unit leaf area decreased as PPFDs increased. Net photosynthetic rates (Pn) increased from 2.7 μmol·m-2·s-1 under 150 PPFD to 5.7 μmol·m-2·s-1 under 450 PPFD, then slightly decreased to 5.5 μmol·m-2·s-1 under 650 PPFD. The highest net photosynthetic rate was not associated with higher intercellular CO2 concentrations (Ci) and stomatal conductance (gs) as plants grown under 250 PPFD had the highest (Ci) (259 ppm) and gs (0.1 mol·m-2·s-1), which suggests that photosynthetic enzymes could play a increasing role under 450 PPFD. Plant quality, however, was not necessarily correlated with the Pn because only those grown under 250 PPFD had appropriate heights, large and dark green leaves, and well-spread branches, and thus were graded higher than plants grown under the other PPFDs. This study shows that fine-tuning production light level is important for high quality Ficus benjamina production.

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Haijie Dou, Genhua Niu, and Mengmeng Gu

-band absorption spectrum that tails into the green light wavelength ( Smith et al., 2017 ). Consistently, plant responses to green light showed a tendency to counteract blue or red light-induced responses, such as inhibition of stem elongation, stomatal opening

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J.G. Carew, K. Mahmood, J. Darby, P. Hadley, and N.H. Battey

The effects of temperature, photosynthetic photon flux density (PPFD) and photoperiod on vegetative growth and flowering of the raspberry (Rubus idaeus L.) `Autumn Bliss' were investigated. Increased temperature resulted in an increased rate of vegetative growth and a greater rate of progress to flowering. Optimum temperatures lay in the low to mid 20°C range. Above this the rate of plant development declined. Increased PPFD also advanced flowering. While photoperiod did not significantly affect the rate of vegetative growth, flowering occurred earliest at intermediate photoperiods and was delayed by extreme photoperiods. These responses suggest that there is potential for adjusting cropping times of raspberry grown under protection by manipulating the environment, especially temperature.

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Jan M. Kossowski and David W. Wolfe

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.

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Mengmeng Gu, James A. Robbins, Curt R. Rom, and Hyun-Sug Choi

experiments. Expt. 1: light response (A/PPFD) of four well-watered birch genotypes Six trees of similar size were selected for each genotype and the experiment was conducted on the 8, 9, and 10 Sept. 2004. Gas exchange measurements were taken between

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Jyotsna Joshi, Geng Zhang, Shanqi Shen, Kanyaratt Supaibulwatana, Chihiro K.A. Watanabe, and Wataru Yamori

to cultivate many vegetables (especially, sun-type plant species), including tomato, paprika, and cucumber, under such low light intensities in a PFAL because they require higher light intensities for growth. The light–response curve of the

Free access

Donald J. Makus* and Gene E. Lester

Field-grown mustard greens, Brassica juncea, were used to validate several observations of a greenhouse study which reported nutrient changes in mustard greens grown, in part, under ambient and reduced light. The cultivar Florida Broadleaf was transplanted into a Hildago sandy clay soil near Weslaco, Texas (26° 08' Lat.) on 6 Nov 2003. Greens were fertigated with 30 kg·ha-1 of N on 1 Dec. Plants 14 days before harvest were grown under the following four light regimes: (1) continuous ambient light; (2) 7 days of 50% shade then 7 days of ambient light; (3) 7 days of ambient light then 7 days of 50% shade; and (4) 14 days of 50% shade. Cumulative solar light was 28.9 and 19.4 kW/m2 during the first and second 7 days, respectively. Measured cumulative light, as PPFD, for treatments 1-4 were 108, 67, 78, and 44 mm·m-2·s-1, respectively. Plants were harvested at 0800, 1100, and 1400 h on 2 Jan. 2004. Shade during the last 7 days generally evoked the greatest responses. Increased shade duration did not significantly effect the agronomic performance, but did increase leaf total carotenoids, chlorophylls, water content, and reduced total ascorbate levels. As time of daylight progressed, sample plant weight and average leaf weight decreased in shaded plants only. Free ascorbic acid, chlorophyll a:b ratio, and the chlorophyll to carotenoid ratio decreased with time of day. Cumulative sunlight, as PPFD, was significantly correlated with total ascorbate (fresh weight basis), chlorophyll a:b ratio, and plant weight (P < 0.06) and negatively correlated with chlorophylls and total carotenoids (dry weight basis). Thus, cloudy weather prior to harvest can reduce leaf Vitamin C and alter leaf greenness

Open access

Geoffrey Weaver and Marc W. van Iersel

supplemental light combined reaches a specified threshold PPFD , and the lights are turned off if sunlight alone exceeds this threshold PPFD . Photosynthetic light responses can generally be described as concave functions of PPFD . The efficiency of