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Haijie Dou, Genhua Niu, and Mengmeng Gu

photosynthesis, morphology, and secondary metabolism ( Amaki et al., 2011 ; Brazaityte et al., 2016 ). The development of light-emitting diode (LED) technology provided researchers opportunities to regulate plant yield and nutritional quality using different

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Jeff L. Sibley, D. Joseph Eakes, Charles H. Gilliam, and William A. Dozier Jr.

Net photosynthesis (Pn), stomatal conductance (Cs), transpiration (Ts), and water use efficiency (WUE) were determined with a LICOR 6250 Portable Photosynthesis System for four cultivars of Acer rubrum L. under light intensities ranging from 300 to 1950 μmol·m-2·sec-1 photosynthetically active radiation (PAR). As PAR increased, there was a linear relationship for Pn, Cs, and Ts for the cultivars `Franksred' (Red Sunset TM) and `October Glory'. In contrast, the cultivars `Schlesingeri' and `Northwood' had quadratic relationships for Pn and Cs as PAR increased. Ts was quadratic for `Schlesingeri' and had a linear relationship for `Northwood.' WUE was quadratic for each of the four cultivars.

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Susanna Marchi, Luca Sebastiani, Riccardo Gucci, and Roberto Tognetti

Net photosynthesis, dark respiration, chlorophyll and carbohydrate content, and leaf and shoot growth in plants of evergreen olive (Olea europaea L.) grown under controlled conditions were measured to assess changes in carbon balance during leaf development of the 6th, 12th, and 16th node (from the base, first flush) through expansion to maturity. Shoot and leaves expanded in a sigmoid pattern with differences among nodes. Photosynthesis varied with leaf development; young leaves had low CO2 assimilation rates that were reflected in their chlorophyll concentration. Net daily CO2 assimilation was negative in young expanding leaves. The sink-source transition, defined to be the time when the increase in daily carbohydrate exchange rate exceeds the daily increase in leaf carbohydrate content, occurred before full leaf expansion, between 10% and 30% expansion depending on the node.

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Lailiang Cheng, Sunghee Guak, and Leslie H. Fuchigami

76 ORAL SESSION 12 (Abstr. 078–083) Photosynthesis

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Woei-Jiun Guo and Nean Lee

In this study, effects of leaf age (20 to 240 days), plant age (4, 8, and 14 months after deflasking), and various day/night temperature regimes (16 to 33 °C) on photosynthesis of Phalaenopsis amabilis L. Blume var. formosa Shimadzu (Phal. TS97) leaves were investigated. The diurnal net CO2 uptake in Phal. TS97 leaves was measured and integrated to obtain total net CO2 uptake, which represents photosynthetic efficiency in plants performing crassulacean acid metabolism (CAM). Under all conditions, Phal. TS97 leaves performed typical CAM photosynthesis and reached their highest net CO2 uptake rate, ≈6 μmol·m-2·s-1, after 3 to 4 hours in the dark under a 12-hour photoperiod. When grown under 30 °C day/25 °C night temperature, the total net CO2 uptake of leaf increased with maturation and was highest at 80 days old, 20 days after full expansion. The CAM photosynthetic capacity of mature leaves remained high after maturation and began to decline at a leaf age of 240 days. The trend was consistent with malate fixation but the highest nocturnal malate concentration was observed in 100-day-old leaves. Young leaves or leaves from small juvenile plants had higher daytime CO2 fixation compared to mature leaves or large plants, suggesting that Phal. TS97 leaves progressed from C3-CAM to CAM during the course of maturation. The second newly matured leaf from the top had the highest net CO2 fixation when the newest leaf was 8 cm in length. Although plant age did not influence total CO2 uptake in the leaf, photosynthetic efficiency of leaves in small younger plants was more sensitive to high light intensity, 340 μmol·m-2·s-1 photosynthetic photon flux. The day/night temperature of 32/28 and 29/25 °C resulted in the highest total net CAM CO2 fixation in vegetative Phal. TS97 plants than higher (33/29 °C) and lower temperatures (21/16 °C).

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Keith T. Birkhold, Karen E. Koch, and Rebecca L. Darnell

Carbon dioxide exchange, dry weight, C, and N content of `Bonita' and `Climax' blueberry (Vaccinium ashei Reade) fruit were measured from anthesis through fruit ripening to quantify developmental changes in amounts of imported C and N required for fruit development. Net photosynthesis occurred in fruit of both rabbiteye cultivars from petal fall through color break. During this time, fruit net photosynthesis declined from 16 μmol CO2/g fresh weight (FW) per hour for `Bonita' and 22 μmol CO2/g FW per hour for `Climax' to 0.2 μmol CO2/g FW per hour for both. Dark respiration for both cultivars declined following petal fall from 16 μmol CO2/g FW per hour to 3 μmol CO2/g FW per hour before increasing at fruit ripening to 9 μmol CO2/g FW per hour. Fruit C content was constant at 0.43 mg C/mg dry weight (DW) throughout development, while N content declined from 0.05 mg N/mg DW at petal fall to 0.01 mg N/mg DW at ripeness. DW accumulation and respiration accounted for 63% and 37%, respectively, of the total C requirement for fruit development. Fruit photosynthesis was estimated to contribute 15% of the total C required for fruit development in both cultivars; however, fruit photosynthesis supplied 50% of the C required during the first 10 days after bloom and 85% during the 5 days after petal fall. This large, early contribution of C from fruit photosynthesis may aid in the establishment of fruit until the current season's vegetative growth can supplement plant carbohydrate reserves in providing C for fruit development.

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Louis Anella and Thomas H. Whitlow

Changes in photosynthesis and root morphology during flooding were studied in container-grown 2- to 3-year-old Acer rubrum L. saplings. The seed was collected from opposite ends of a hydrologic gradient: two upland xeric sites [the George Washington National Forest in Page County, Va. (38°25'N, 78°35'W), and the Robinson Forest in Perry County, Ky. (37 °9'N, 83°7'W)] and a floodplain hydric site [the Presquile National Wildlife Refuge along the James River in Chesterfield County, Va. (37°21'N, 77°16'W)]. Each xeric site, containing various half-sib families (maternal parent known, paternal parent from one or more sources), was compared to a different hydric site half-sib family. After 1 week of flooding, the xeric-site trees had lower net photosynthesis than the hydric-site trees and remained significantly lower for the duration of the study. After an initial drop, hydric-site plants showed a recovery in net photosynthesis, indicating a greater ability to acclimate to a flooding stress. Seventy-one percent of the hydric-site plants developed adventitious roots and all retained their leaves. Xeric-site plants did-not develop adventitious roots and 61% were defoliated after 60 days of continuous flooding. The results indicate ecotypic differentiation in physiological response between Acer rubrum populations collected from opposite ends of a hydrologic gradient.

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Chafik Hdider and Yves Desjardins

To identify the physiological and biochemical events leading to the negative effects of sucrose in culture medium on the photosynthetic capacity of plantlets cultivated in vitro, time-course changes in photosynthesis, metabolize pool sizes, and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) activity were investigated in strawberry (Fragaria × ananassa Duch. cv. Kent) plantlets following their transfer to medium with or without sucrose. When the plantlets grown in medium without sucrose were transferred to a similar medium with 30 g sucrose/liter, their net photosynthesis decreased and their level of phosphorylated compounds increased with time. In addition, initial Kcat, total Kcat, and the activation state of Rubisco decreased in these plantlets. Conversely, when the plantlets grown in medium with 30 g sucrose/liter were transferred to a similar medium without sucrose, their net photosynthesis slowly increased with time and their level of phosphorylated compounds slowly decreased. A slow increase with time of initial Kcat, total Kcat, and the activation state of Rubisco was also observed in these plantlets. The results of the present research suggest that the reduced photosynthetic capacity of strawberry plantlets cultivated in vitro in the presence of sucrose was the consequence of reduced Rubisco efficiency due to its deactivation and the possible presence of a putative tight binding inhibitor.

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E.D. Leonardos, M.J. Tsujita, and B. Grodzinski

The influence of irradiance, CO2 concentration, and air temperature on leaf and whole-plant net C exchange rate (NCER) of Alstroemeria `Jacqueline' was studied. At ambient CO2, leaf net photosynthesis was maximum at irradiances above 600 μmol·m-2·s-1 photosynthetically active radiation (PAR), while whole-plant NCER required 1200 μmol·m-2·s-1 PAR to be saturated. Leaf and whole-plant NCERs were doubled under CO2 enrichment of 1500 to 2000 μl CO2/liter. Leaf and whole-plant NCERs declined as temperature increased from 20 to 35C. Whereas the optimum temperature range for leaf net photosynthesis was 17 to 23C, whole-plant NCER, even at high light and high CO2, declined above 12C. Dark respiration of leaves and whole plants increased with a Q10 of ≈2 at 15 to 35C. In an analysis of day effects, irradiance, CO2 concentration, and temperature contributed 58%, 23%, and 14%, respectively, to the total variation in NCER explained by a second-order polynomial model (R 2 = 0.85). Interactions among the factors accounted for 4% of the variation in day C assimilation. The potential whole-plant growth rates during varying greenhouse day and night temperature regimes were predicted for short- and long-day scenarios. The data are discussed with the view of designing experiments to test the importance of C gain in supporting flowering and high yield during routine harvest of Alstroemeria plants under commercial greenhouse conditions.

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Marc W. van Iersel and Bruce Bugbee

Benzimidazoles are effective and widely used fungicides, but they may be phytotoxic. We studied the effects of a single drench application of six benzimidazoles and one acetanilide fungicide on photosynthetic gas exchange, growth, development, and nutrient levels of four species of bedding plants in twenty growth-chamber and four greenhouse studies. Daily carbon gain and carbon-use efficiency were calculated from continuous crop gas-exchange measurements in the growth chambers. The maximum labeled rate of Benlate DF caused a 7- to 10-day decrease in net photosynthesis and daily carbon gain in transplants of all species. It also caused pronounced interveinal chlorosis and a 2- to 3-day delay in flowering. Growth of Benlate DF-treated plants was reduced more at high (90%) than at low (60% to 80%) relative humidity. Benlate DF had severe effects on 2-week-old petunia (Petunia ×hybrida) seedlings in plug flats, reducing photosynthesis 25% to 57%. Cleary's 3336 WP decreased photosynthesis in some trials. Benlate DF reduced photosynthesis within 24 hours, but 3336 WP effects did not become apparent until 1 week after the treatment. This suggests different modes of inhibition. 3336 WP also caused leaf-tip and marginal chlorosis in impatiens (Impatiens wallerana). Mertect 340-F was extremely phytotoxic but is not labeled for drench applications (it was included because of its chemical similarity to other benzimidazoles). The only benzimidazole fungicide that did not reduce photosynthesis was Derosal, but it caused slight interveinal chlorosis in some studies with petunia. Benlate DF and Derosal decreased leaf Ca levels. Subdue (or metalaxyl), an acetanilide fungicide, did not affect photosynthesis or cause any visual symptoms. Our results indicate that some benzimidazole fungicides can cause growth reductions and visual damage in bedding plants.