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R. Paul Schreiner and Carolyn F. Scagel

observed that the frequency of arbuscules in grape roots increases dramatically from early summer to midsummer in concert with increasing leaf area and photosynthetic capacity of vines, whereas total AMF colonization in roots does not change ( Schreiner

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Elisa Solis-Toapanta and Celina Gómez

production could be as productive as those grown constantly under higher DLIs. Based on our two goals, the objective of this study was to quantify and compare growth and photosynthetic capacity over time of two basil cultivars grown hydroponically under

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De Yue, André Gosselin, and Yves Desjardins

Photosynthesis and growth of in vitro-cultured strawberry plantlets (Fragaria × ananassa Duch. cv Kent) were investigated during a 4-week in vitro culture in a rooting medium and a 4-week ex vitro period. The leaves formed in vitro on a medium containing sucrose developed a positive photosynthetic capacity. At transplanting to the ex vitro environment, their photosynthetic rate was 12.76 μmol CO2/m2 per second, which was as high as that of leaves generated and grown in the greenhouse. During the ex vitro period, photosynthetic rates of in vitro-generated leaves decreased and dark respiration rates increased. However, in vitro leaves were photosynthetically active throughout the 4 weeks ex vitro. In the first 2 weeks of the ex vitro period, in vitro-generated leaves had an important contribution to the overall plantlets' photosynthetic capacity.

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David J. Ballantyne

In a greenhouse experiment involving 13 hardy azalea (Rhododendron spp.) cultivars, `Noordthiana' and `Treasure' had the highest rate of shoot elongation and the highest photosynthetic capacity (Pcap) during the summer. In winter, `Treasure' had a high rate of shoot elongation and Pcap, but `Noordthiana' had a high rate of shoot elongation and low Pcap. Long days or GA3 sprays stimulated shoot elongation but not Pcap of certain cultivars. GA3 was effective in stimulating shoot elongation of `Vuyk's Scarlet' if plants were given supplemental photoperiods under natural winter (short) photoperiods. Cultivars with a high rate of shoot elongation and Pcap likely will produce salable plants in a shorter time period than slower growing cultivars because less time elapses between prunings. Production time can be decreased further with GA3 sprays, especially with GA3 applications in combination with supplemental photoperiods during the short days of winter. Chemical name used: gibberellic acid (GA3).

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Paul W. Foote, J. Scott Cameron, and Stephen F. Klauer

Leaf-area based CO2 assimilation rate (ALA as an Indicator of genotypic differences in photosynthetic capacity is questioned on the basis of correlations found between ALA and specific leaf weight and small leaf size. To address this question of photosynthetic apparatus concentration In F. chiloensis genotypes differing significantly in ALA, visual image analysis software was used to quantify a number of leaf anatomy parameters. In 1991 and 1992, after gas exchange measurements in the field, leaf tissue was prepared In cross-sections and leaf clearings for light microscopy. Cross-sections were used to measure internal anatomical parameters and clearings for vein and stomatal densities.

Analysis of variance of 1991\92 measurements showed significant genotypic variation for leaf veination, leaf thickness, palisade cell length, cross-sectional area In mesophyll tissue and internal air space. Differences in stomatal density were observed in 1991. None of the anatomical parameters measured were correlated with ALA. This suggests that the concentration of physical apparatus Is not the major source of variation In ALA among these eight genotypes.

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William L. Bauerle, Joseph D. Bowden, and Geoff G. Wang

This study set out to test the hypothesis that the development in the capacity for the maximal rate of ribulose-1,5-bisphosphate carboxylase/oxygenase (VCmax) and the maximum regeneration rate of ribulose-1,5-bisphosphate (Jmax) per unit mass is proportional to the growth temperature under which the leaf develops and to investigate whether the capacity for photosynthetic acclimation to temperature varies genetically within a species by testing genotypes that originated from diverse thermal environments. Acer rubrum L. (red maple) genotypes were subjected to short-term and long-term temperature alteration to investigate the photosynthetic response. We minimized the variation of within-crown light gradients by growing trees in open grown field conditions and controlled temperature on a crown section basis. Thus, we singled out the temperature acclimation affects on the photosynthetic temperature optimum. In response to temperature acclimation, the genotype from the northern United States downregulated both VCmax and Jmax and had a 5 and 3 °C lower temperature optimum than the genotype native to the southern United States. The activation energy increased and was higher for Jmax than for VCmax in both genotypes. With respect to respiration, both genotypes downregulated about 0.5 μmol·m-2·s-1. Although respiration was lower, the increased energy of activation in response to growth temperature resulted in a decrease in maximum net photosynthetic rate (Amax) under saturating light and CO2. The results illustrate that the photosynthetic capacity adjusted in response to growth temperature but the temperature optimum was different among genotypes.

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Sydney Lykins, Katlynn Scammon, Brian T. Lawrence, and Juan Carlos Melgar

without protective overhead structures such as high tunnels or shade nets ( Strik et al., 2007 ). Currently, a greater understanding of cultivar-specific responses to increasing irradiance is needed to avoid reduced photosynthetic capacity caused by high

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Lie Li, Yu-xin Tong, Jun-ling Lu, Yang-mei Li, and Qi-chang Yang

photosynthetic capacity. In this study, increases were demonstrated in lettuce shoot fresh weight/dry weight and P n when lettuce was grown under RBG and RBO, whereas only an increase in lettuce shoot fresh weight/dry weight was found under RBFR ( Fig. 1

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Guohai Xia, Lailiang Cheng, Alan Lakso, and Martin Goffinet

manipulated by thinning ( Haller and Magness, 1925 ; Magness, 1928 ; Magness and Overley, 1929 ; Preston, 1954 ). The small leaf area to fruit ratio coupled with low leaf photosynthetic capacity under low N supply clearly indicates that the low N trees are

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J.S. Seron, R.J. Ferree, S.L. Knight, M.A.L. Smith, and L.A. Spomer

Tolerance of increased salinity by tomato is of great importance to the tomato processing industry, where increased conductivity of up to 6 dS m-1 is used to increase specific yield components. A new line of miniature dwarf tomato, Lycopersicon esculentum Mill. cv. Micro Tom, was evaluated for photosynthetic response to elevated salinity. Tomatoes were grown in solution batch culture and subjected to constant salt treatments of 2.4 (control), 7.6, 12.8, or 18 dS m-1. Weekly photosynthetic measurements were made beginning week 4 on the most recent fully open leaf or leaf opposite a fruit. Net photosynthesis decreased across all salt treatments over the last six weeks of sampling. As salinity level increased, net photosynthesis decreased compared to the control. The 18 dS m-1 treatment reduced net photosynthesis relative to 12.8 and 7.6 dS m-1. Although salinity increased succulence, limitations to net photosynthesis were due to diminished utilization of intercellular CO2, rather than reduced internal CO2 concentration or stomatal conductance.