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Mokhles A. Elsysy, Michael V. Mickelbart, and Peter M. Hirst

study of the effect of fruiting and biennial bearing potential on spur quality and leaf gas exchange in apple. Bearing classification was based on experience with these cultivars. This experiment used mature trees growing on dwarfing ‘Budagovsky 9’ (B.9

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Manuel G. Astacio and Marc W. van Iersel

, MA) was clamped onto the uppermost, fully expanded leaf of a plant before treatment and leaf gas exchange was recorded every 5 min. Once stable readings were achieved and pretreatment data were gathered for 30 min, treatments were applied and leaf gas

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S.M. Scheiber, R.C. Beeson Jr, J. Chen, Q. Wang, and B. Pearson

growth but decreased water use efficiency. The objectives of this study were to: 1) evaluate growth responses and leaf gas exchange of the annual bedding plant coleus in relation to irrigation frequency and quantity, 2) develop and examine water budgets

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Md. Jahedur Rahman, Haruhisa Inden, and Masaaki Kirimura

nutrient solution may result in serious yield reduction. Furthermore, overirrigation and prolonged soil saturation can cause disease in plant roots or root rot. However, different irrigation timing may have an effect on yield by affecting leaf gas exchanges

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Thomas E. Marler and Leah E. Willis

Leaf gas exchange characteristics for 16 species of cycad were determined under field conditions in Miami, Fla. Net CO2 assimilation (ACO2) ranged from 4.9 μmol·m-2·s-1 for Lepidozamia peroffskyana Regel to 10.1 μmol·m-2·s-1 for Zamia furfuracea L. fil. in Aiton. Stomatal conductance to H2O (gs) was more variable, ranging from 85 mmol·m-2·s-1 for Cycas seemannii A. Br. to 335 mmol·m-2·s-1 for Encephalartos hildebrandtii A. Br. & Bouche. Transpiration (E) ranged from 1.7 mmol·m-2·s-1 for Cycas chamberlainii W.H. Brown & Keinholz to 4.8 mmol·m-2·s-1 for Encephalartos hildebrandtii. Highly variable E was more controlling of water-use efficiency than the less-variable ACO2. The difference between air and pinnae temperature ranged from 0.3 to 1.6 °C and was inversely related to mean gs among the species. The values within geographic regions representative of the native habitats of the species were highly variable. For example, two of the African species exhibited the highest and lowest values of water-use efficiency in the survey. Leaf gas exchange for the four largest species with arborescent growth form was less than that for the three small species with subterranean or short bulbous growth form. The diurnal variation in leaf gas exchange for Zamia furfuracea exhibited a two-peaked pattern with a distinct midday depression in ACO2 and gs. The ratio of dark respiration to maximum ACO2 for Zamia furfuracea was 0.04. As a group, the values for ACO2 and gs for these cycads ranked at the lower end of the range for all plants species.

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Rosana Moreno, Diego S. Intrigliolo, Carlos Ballester, Cruz Garcerá, Enrique Moltó, and Patricia Chueca

. Between each experimental unit tree a barrier tree was left. Plant water status and leaf gas exchange determinations. Plant water status and leaf gas exchange were monitored in trees sprayed with water plus adjuvant and those sprayed with the highest dose

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Juan Carlos Díaz-Pérez

., Ramsey, NJ). Leaf gas exchange and photosystem II efficiency. Simultaneous measurements of leaf gas exchange (net photosynthesis, g S , transpiration, and internal CO 2 concentration) and fluorescence determined as photosystem II (PSII) efficiency were

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Thomas E. Marler and Michael V. Mickelbart

Long-term effects on stomatal conductance of mechanical stress from repeated clamping of a porometer leaf cuvette to laminae of avocado (Persea americana Miller), carambola (Averrhoa carambolu L.), hibiscus (Hibiscus rosa-sinensis L.), mango (Mangifera indica L.), and sugar apple (Annona squamosa L.) plants were determined under glasshouse conditions. Following 10 weeks of applying the mechanical stimulus seven times during every 4th day to mature leaves, stomatal conductance was lower than for untreated leaves of all species except mango. Similarly, following 10.5 weeks of applying the stimulus one time every 4th day to expanding leaves of avocado, carambola, hibiscus, and sugar apple, stomatal conductance was lower than for untreated leaves of the same age in all species except hibiscus. Carambola and sugar apple were more sensitive to the mechanical stress than the other species. Thus, the indirect effect of leaf chamber clamping on gas exchange should be known before any conclusions are formulated regarding environmental, cultural, or genetic effects on gas exchange. Random leaf samples from a canopy instead of measurements on a fixed set of leaves may be more appropriate for repeated determinations of leaf gas exchange on a set of plants.

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Thomas E. Marler and Yasmina Zozor

Growth and leaf gas-exchange responses of carambola (Averrhoa carambola L.) seedlings to wind or seismic stress were studied under glasshouse conditions. Forty days of twice daily seismic stress applied for 10 seconds consistently reduced carambola height, leaf area, dry weight, relative growth rate, and leaf-area ratio, but increased trunk cross-sectional area compared with plants receiving no seismic stress. Fifty-one days of wind load reduced plant height, leaf area, dry weight, trunk cross-sectional area, net assimilation rate, relative growth rate, leaf-area ratio, and stomatal conductance compared with plants receiving no wind stress. Morphological appearance was similar for plants receiving wind or seismic stress. Net CO2 assimilation of carambola leaflets was reduced by 30 minutes of wind load for up to 6 hours following the stress. Results suggest that wind may reduce carambola growth at least partially by influencing leaf gas exchange or by the mechanical stress associated with wind.

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Thomas E. Marler and Yasmina Zozor

Leaf gas-exchange responses of A. souamosa seedlings to salinity were studied in sand culture in a series of glasshouse experiments. Trees were irrigated with a complete nutrient solution as the control, or with this solution amended to 3 or 6 dS/m with sea salt. Inhibition of net CO2 assimilation, stomatal conductance of CO2, and transpiration was apparent 14 days after treatments were imposed, and continued to decline until day 30 to 35. The diurnal pattern of leaf gas exchange was not altered by salinity. Salinity reduced CO2, light energy, and water use efficiencies. Dark respiration and internal partial pressure of CO2 were unaffected by salinity stress. Results indicated that substrate salinity inhibited photosynthesis of A. souamosa via limitations on mesophyll capacity for CO2 assimilation and had little effect on gas phase limitations.