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Daniel Leskovar and Yahia A. Othman

measured 15 weeks after the N application in each year. Gas exchange measurements were conducted between 1100 and 1300 hr from two fully expanded leaves. Gas exchange measurements were determined using a portable photosynthesis system (LI-6400XT; LI

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Jean-Pierre Privé, Lindsay Russell, and Anita LeBlanc

net photosynthesis (Pn) were achieved at a higher frequency of kaolin particle film application and that this was particularly the case at leaf temperatures exceeding 35 °C ( Privé et al., 2007 ). Ultraviolet damage and photoinhibition can be additive

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Ajmer S. Bhagsari and Doyle A. Ashley

Field experiments with 15 sweet potato [Ipomoea batatas L. (Lam.)] genotypes were conducted to study the physiological basis of yield in 1981 and 1982. The leaf area index differed significantly among the sweet potato genotypes during early and late phases of growth, hut showed an inconsistent relationship with yield. Single leaf net photosynthesis ranged from 0.74 to 1.12 mg CO2/m' per sec. Canopy photosynthesis for sweet potato genotypes differed significantly in 1981, but not in 1982. It ranged from 0.81 to 1.16 mg CO2/m2 per sec in Aug. 1981. and from 0.63 to 0.88 mg CO2/m2 per sec in 1982. Four hours after “C-labeling, 14C-assimilate translocation from the treated leaf ranged from 21% to 46%, but did not differ significantly among the genotypes. At final harvest, harvest index [HI, defined as (storage root yield/total biological yield) × 100] of the genotypes varied from 43% to 77% and 31% to 75% for 1981 and 1982, respectively. Canopy photosynthesis during September was significantly correlated with storage root dry matter yield (r = 0.54*) in 1981 and with phytomass (above-ground biomass plus storage roots) (r = 0.60*) in 1982. Both phytomass and HI were significantly correlated with storage root matter yield. Canopy photosynthetic evaluation of sweet potato germplasm may be-more relevant when the storage root sinks are at an advanced stage of development. Our study suggests that yield is poorly predicted by Pn, particularly when the genotypes have different leaf sizes.

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Ajmer S. Bhagsari and Silas A. Harmon

Abstract

Field experiments were conducted during 1979 and 1980 growing seasons with sweet potato [Ipomoea batatas (L.) Lam.] genotypes at different stages of growth to determine leaf net photosynthetic rates (Pn) and photosynthate partitioning patterns. Net photosynthesis was measured in an open system with an infrared analyzer on the youngest and the fully expanded leaves still attached to the plant. Photosynthesis rates differed significantly in both years. Photosynthesis varied from 19.1 to 32.4 mg CO2dm−2hr−1 in 1979 and from 25.8 to 36.9 mg CO2dm−1hr−1 in 1980. A new selection, 75-96-1, averaged highest both years. Percentages of photosynthate partitioning to storage roots also differed significantly. About 45 days after planting, ‘Centennial’ and ‘Georgia Jet’ diverted the highest percentage, about 28%, of the total dry matter to the storage roots. But ‘Georgia Red’ diverted the highest percentages of photosynthate (51.0 and 56.4) to the storage roots 75 and 90 days after planting, respectively. Photosynthate partitioning to storage roots ranged from 11.2 to 56.4%, 90 days after planting. Final root yield correlated significantly (r = 0.69 to 0.87) with photosynthate partitioning at all stages of growth. During 1980, Pn and total dry matter yield also were significantly correlated. Harvest index was significantly correlated (r = 0.89) with final storage root yield. But Pn did not significantly correlate with either storage root yield or photosynthate partitioned to roots. Stomatal density was 2 to 3 times more on the abaxial than the adaxial surface of the leaves. Percentages of neither leaf nitrogen nor chlorophyll content of leaves differed significantly. High-yielding genotypes generally initiated storage root formation earlier and also partitioned more photosynthate to storage roots than low-yielding genotypes.

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Timothy E. Elkner and D. C. Coston

Abstract

One of the most important aspects of designing an experiment is determining sample size. Without prior experience, estimation of the amount of variation that will be encountered during data collection is difficult. This information is necessary to decide the number of replicates needed. Recently, Marini (1985) and Marini and Trout (1984) have published reports on the sample size needed to determine treatment effects in peach tree growth and yield studies. However, this type of information is lacking for sample sizes required to detect differences in net photosynthesis in peach. This note attempts to assist researchers in determining correct sample size.

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Stephanie Brown and Alejandro Ching

A photosynthesis study was conducted on seedlings of Lycopersicon esculentum L. cv. “Traveller 76” subjected to natural, clear, blue and red color irradiations to predict and evaluate harvest time and yield potential. Photosynthesis (PS) rates were higher on clear and red irradiated transplants with 16.1 and 12.4 μMol/m2/s, respectively, for two weeks of treatment. Blue irradiation showed lowest PS rate with 2.2 μMol/m2/s. For the third and fourth weeks of treatment, PS rate increased to 10.9 and 13.5 μMol/m2/s, respectively, on blue light treated transplants, while red, clear and natural light treatments decreased. CO2 appears to be lowest at high PS rate under these treatments. Transplants treated with blue and red lights were taller and thicker around the stem. Clear and natural lights were shorter, but with a larger root biomass. PAR (Photosynthetically Active Radiation) was highest at noon under open natural light with 1108.8 μE/s/m2, but also high for blue, red and clear lights when compared to earlier or later time. The lowest PAR was shown for blue and red lights.

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Manuela Zude-Sasse, Ulrich Hartmond, Georg Ebert, and Peter Lüdders

Soil flooding reduces partial pressure of oxygen (pO2) in the root zone and often results in a reduction in photosynthesis and growth. In greenhouse studies, rooted stem cuttings of the mango (Mangifera indica L.) rootstock selection 13/1 were exposed to anoxia by saturating the root zone with N2 for up to 52 h. Reduced pO2 in the root zone affected the energy status of the roots and particularly enhanced the phosphorylated and nonphosphorylated pyridine nucleotide charges—the ratio of reduced Nicotinamide-adenine-dinucleotides [NAD(P)H] to total Nicotinamide-adenine-dinucleotide content [oxidized NAD(P)+ plus NAD(P)H]—that drive the redox reaction rates in cell metabolism. Also, the pyridine nucleotide charges in leaves were enhanced, while the photosynthetic rate decreased following reduction in pO2 in the root zone. During up to 4 h of reduced pO2, the ratio of internal CO2 concentration in the mesophyll to ambient CO2 concentration was unchanged. This implies a nonstomatal influence on photosynthesis. In addition, light saturation of photosystem II occurred at lower irradiance (470 μmol·m-2·s-1) resulting in reduced maximum photochemical efficiency below that of the high pO2 controls. After 28 h of reduced pO2, NAD(P) charges in the leaves returned to normal, diminishing its potential effect on net photosynthetic rate.

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Tonghua Pan, Juanjuan Ding, Gege Qin, Yunlong Wang, Linjie Xi, Junwei Yang, Jianming Li, Jing Zhang, and Zhirong Zou

400 μmol·mol –1 , and this value is projected to double by the end of 21st century ( Urban et al., 2014 ). However, in a closed greenhouse, as plants absorb CO 2 for photosynthesis, CO 2 levels may fall to as low as 150 μmol·mol –1 in bright

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David J. Ballantyne

The influence of photosynthetic photon flux density (PPFD) and gibberellic acid (GA3) sprays on shoot elongation was determined for `Coral Bells' (Kurume or R. obstusum hybrid), `Fashion' (Glen Dale or R. indicum × Kurume hybrid), `Hexe' (R. obtusum × R. simsii hybrid), `Hinocrimson' (Kurume or R. obtusum hybrid), `Hinodegiri' (Kurume or R. obtusum hybrid), and `Red Wing' (Brooks hybrid) azalea. GA3 at 1 mm was more effective in stimulating shoot elongation of `Coral Bells', `Fashion', `Hinodegiri', and `Red Wing' than of `Hexe' or `Hinocrimson'. GA3 sprays were more effective in stimulating elongation when applied to plants growing at irradiance levels of 350 μmol·s-1·m-2 than to plants growing at either 200 or 100 μmol·s-1·-2. Gross photosynthesis of leaf segments was higher for a slow-growing cultivar (Hinocrimson) than for a faster-growing cultivar (Fashion). `Hinocrimson' produced stouter shoots (greater dry weight/cm) than did `Fashion'.

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Connie S. Bozarth, Robert A. Kennedy, and Kurt A. Schekel

Abstract

For all leaf ages of Rosa hybrida L. cv. Samantha, maximum photosynthetic rates were reached at irradiances of 450 to 500 μE m−2sec−1. The magnitude of this response decreased from 20.6 mg CO2 dm−2hr−1 in the youngest leaves studied to 15.4 mg CO2 dm−2hr−1 in the oldest. Maximum photosynthetic rates were reached before full leaf expansion. Mesophyll resistance, however, increased with age from 7.8 to 12.5 cm sec−1. CO2 compensation points and dark respiration decreased throughout most of leaf development, but increased slightly at the most advanced developmental ages studied. Photosynthetic enhancement, the percent increase in net photosynthesis at 2% O2 compared to 21% O2, averaged 33% for all leaves. There was no change in the amount of photosynthetic enhancement as leaves aged, indicating that changes in photorespiration were not a major factor in photosynthetic trends over the range of leaf ages examined.