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D.L. Deal, J.C. Raulston, and L.E. Hinesley

Red- and purple-leafed seedlings and clonal material selected for superior color and growth under northern climatic conditions may exhibit progressive color loss and reduced growth rates when exposed to the hot summers and high night temperatures of more southern climates. Studies were conducted to characterize the color loss associated with red-leafed seedlings of Acer palmatum Thunb. (Japanese maple), and to determine to what extent night temperatures affect the dark respiration, growth, and anthocyanin expression of A. palmatum `Bloodgood'. The percentage of seedlings within each of five color classes was determined for five dates from spring to early fall. Significant shifts in class distribution occurred on every evaluation date tested. The class changes contributing the most to these shifts varied with age of leaf material and date. Dark respiration rates increased by 0.09 mg CO2/g leaf dry weight per hour for every 1C rise in temperature, regardless of exposure duration. Dark respiration rates of 0.69 and 1.73 mg CO2/g per hour were found at 14 and 26C, respectively. The greatest amount of growth occurred during weeks 6 through 8 at a night temperature of 14C. Plant growth during this period increased by an average 51%, compared to that at warmer night temperatures. Ultimately, total plant growth at 14C decreased 7%, 19%, and 32% as night temperatures increased from 18 to 22 to 26C. Leaf redness index values at 14 or 18C were from two to seven times greater than those at warmer night temperatures.

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Kathleen B. Evensen and Karen M. Olson

Postproduction quality, net C exchange, and petal abscission in response to ethylene were compared following forcing at 21(day)/16C(night) or 18/13C(18-hour photoperiod) of two cultivars of Pelargonium × domesticum L.H. Bailey. Fewer petals of 2- to 6-day-old florets abscised in response to 60 minutes of 0.7 μl ethylene/liter on plants forced at low temperature than on plants forced at 3C higher temperature. Forcing temperature did not affect floret longevity or the number of florets opening during forcing, but the floral display under simulated consumer conditions was prolonged in low-temperature plants by the continued development of buds. Dark respiration rates at 21C were lower in leaves from plants forced at low temperature than in leaves of plants forced at the higher temperature. Differences in postproduction quality between plants forced at high and low temperatures may have been related to the reduced rate of carbohydrate depletion in low-temperature plants.

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Krishna Nemali and Marc W. van Iersel

[whole-plant net photosynthesis (micromoles per second)] and dark [whole-plant respiration (micromoles per second)]. Approximately 0.4 L·s −1 of air from outside the building was blown into each chamber using a rotary vane blower (DT 3.4; Becker

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Ming Li and Wei-tang Song

hour (h −1 ) during photoperiod and dark period, respectively, and P n,w ′ and R d,w ′ are the real net photosynthetic rate and dark respiration rate of whole-plant (µmol·h −1 /transplant). Substituting Eqs. [3] and [5] into Eq. [1] , e P can

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Jakob Markvart, Eva Rosenqvist, Helle Sørensen, Carl-Otto Ottosen, and Jesper M. Aaslyng

reduction in dark respiration ( Nemali and van Iersel, 2004 ; Xu et al., 2004 ). However, supplemental light is mainly used during the dark period of the year where light conditions during the day and nights are low and the increase in photosynthesis with

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Thomas E. Marler, Michael V. Mickelbart, and Roland Quitugua

Leaves of container-grown papaya (Carica papaya L.) plants were inoculated with papaya ringspot virus (PRV) to determine its influence on dark respiration and photosynthesis. Photosynthetic capacity, apparent quantum yield, ratio of variable to maximum fluorescence from dark-adapted leaves, and photosynthetic CO2-use efficiency were reduced by PRV infection. Internal CO2 partial pressure at ambient external CO2 was not affected, but leaf dark respiration was increased by PRV infection. These results suggest that reduced growth, yield, and fruit quality common in PRV-infected papaya plants is caused, at least partially, by reduced photosynthesis and increased respiration.

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C.S. Hew, T.K. Ong, and W.P. Yap

A circadian rhythm in CO2 production was observed in three cultivars of Anthurium andraeanum Andre (`Jaya', `Fla-range', `Leonette') flowers. The rhythmicity was not affected by light, darkness, and detachment. However, the amplitude was dampened in darkness and after detachment. Spadix respiration accounted for 90% of the total flower respiration. Rhythmicity in CO2 production continued after spathe removal. Less pronounced rhythmicity was observed following spadix removal.

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John Erwin and Esther Gesick

“ k ” was a constant that represented the ratio of the quantum yield ( q ) to the P n at the LCP ( Marino et al., 2010 ). R d (dark respiration) was calculated as the estimated P n (I) when irradiance was 0 μmol·m −2 ·s −1 . Eq. [2] shows P n

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Leonardo Lombardini, Hermann Restrepo-Diaz, and Astrid Volder

locations have dark respiration rate (R d ) values in the range of 0.67 to 1.33 μmol·m −2 ·s −1 of CO 2 , whereas R d in species from the shaded floor of dense forests range from 0.10 to 0.27 μmol·m −2 ·s −1 of CO 2 ( Björkman, 1968 ). Light compensation

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Tania K. Dautlick and Eric Young

One-year-old potted `Jonagold' apple trees on M. 9 EMLA rootstock were chilled in a cold room at 5C for 1320, 3288 or 4464 hours. They were then placed in a 22C greenhouse for forcing. Rate of dark respiration of buds and internodes was measured in vivo using the LICOR LI 6200 portable photosynthesis system. Measurements were taken on each tree at several distances from the shoot apex during the forcing period. The new apical growth was removed from half of the trees when apical growth was 2-4cm. Removal of apical growth did not appear to influence respiration. Respiration of both buds and internodes generally decreased with distance from apex. As budbreak occurred or when trees received excess chilling hours, the effect of distance from apex on respiration decreased. Excess chilling also resulted in greater and more rapid budbreak.