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Cyrus A. Smith, James L. Walworth, Mary J. Comeau, Richard J. Heerema, and Joshua D. Sherman

intercellular space, and reduce leaf thickness and surface area ( Ojeda-Barrios et al., 2012 ). Hu and Sparks (1991) noted that stomatal conductance ( g S ) and net photosynthesis (P n ) were reduced concomitantly by low Zn levels. Heerema et al. (2017

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Francesco Montesano and Marc W. van Iersel

were measured 26 d after the start of the treatments. Leaves were exposed to a photosynthetic photon flux ( PPF ) of 1000 μmol·m −2 ·s −1 and a CO 2 concentration of 400 μmol·mol −1 for at least 20 min, using a portable photosynthesis system (CIRAS-1

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M. Carmen González-Mas, M. José Llosa, Antonio Quijano, and M. Angeles Forner-Giner

Carrizo citrange, which could not surpass 73% ( Fig. 1B ). This could be the result of the incomplete reoxidation of Q A, leading to the downregulation of photosynthesis in comparison with the other rootstocks under assay. In conclusion, based on

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Richard N. Arteca, De-Sheng Tsai, and Carl Schlagnhaufer

Abstract

The effect of root applications of abscisic acid (ABA) on photosynthesis and transpiration in geranium (Pelargonium ×hortorum ‘Glacier Crimson’ Syn. Bruni) cuttings was evaluated using an open infrared CO2 gas exchange system. At concentrations above 3.8 μM ABA there was a reduction in relative growth rate (RGR), transpiration, and photosynthesis 2 days following treatment. Three hours following treatment with 76 μM ABA there was a maximum decrease in both photosynthetic and transpiration rates. Plants which were treated with 76 μM ABA for 6 or 9 hr showed an inhibition in photosynthesis and transpiration 4 days followiing treatment; however, after 6 days there was no difference between treated and control plants. The reduction in transpiration and photosynthesis reported in this paper may have practical value in the shipment and storage of geranium cuttings.

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J. Ryan Stewart, Reid D. Landes, Andrew K. Koeser, and Andrea L. Pettay

evaluate the relative vigor, as indicated by net photosynthesis and plant growth, of three taxa that grow wild in relatively small areas in the United States and may merit use in managed landscapes: Calycanthus occidentalis Hook. & Arn. (western

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Robert D. Marquard

Abstract

Leaf to fruit ratios of 2, 4, 8, and 12 were created on girdled shoots of three cultivars of pecan (Carya illinoensis (Wangenh.) C. Koch). Girdling of fruiting and vegetative shoots reduced net photosynthesis to nearly 30% and 3%, respectively, of the ungirdled “checks.” Differences in photosynthetic rates among the various leaf to nut ratios were not detectable. Two leaves, equivalent to 575 cm2 of leaf area, were sufficient to fill one pecan kernel of ‘Sioux’ or ‘Western’. A ‘Mohawk’ leaf to fruit ratio of 4 produced nuts superior in quality to those supported by two leaves. Girdling tended to increase shoot carbohydrates, and starch accumulation was related to leaf to fruit ratio in ‘Mohawk’.

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John W. Moon Jr.

179 ORAL SESSION (Abstr. 715-722) CROSS-COMMODITY PHOTOSYNTHESIS

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Francesco Loreto, Domenico Tricoli, Mauro Centritto, Arturo Alvino, and Sebastiano Delfine

Short-term fumigation with 1% methanol in air was carried out to investigate effects on the photosynthetic apparatus of horticultural species characterized by leaves with different stomatal distribution. Methanol decreased the photosynthetic capacity of all species. The hypostomatous cherry (Prunus avium L.) was the most sensitive species. Between the two amphistomatous species, the effect was smaller in pepper (Capsicum annuum L. var. annuum) than in melon (Cucumis melo L.). A 4-minute fumigation caused a stronger inhibition of photosynthesis than a 90-second fumigation. The time course of the inhibition of the photosynthetic electron transport following a methanol fumigation of cherry leaves suggests that methanol starts inhibiting photosynthesis and photorespiration after ≈60 seconds and that the effect is complete after 180 seconds. This inhibition is not permanent, however, since gas-exchange properties recovered within 24 hours. Methanol vapor effects were greatest when leaves were fumigated on the surfaces with stomata. However, fumigation with methanol does not affect stomatal conductance. Therefore, inhibition of photosynthesis following methanol fumigation can be attributed to a temporary inhibition of biochemical reactions.

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Z. P. Tu, A. M. Armitage, and H. M. Vines

Abstract

Cineraria plants (Senecio cruentus DC) were transplanted into medium either with or without a hydrogel (polyethylene oxide). Half the plants in each medium were treated with a film-forming antitranspirant while half were not. Plants then were placed either in a clear glasshouse or a shaded glasshouse (40% shade), and no additional water was applied. Water loss was lowest for plants where both the foliage and medium were treated, whereas control plants (no treatment) lost water most rapidly regardless of light intensity. Plants which received only the hydrogel were similar in water loss to control plants at both light intensities. As water stress developed, net photosynthesis (Pn) decreased, reaching a zero rate at wilting; however, Pn measurements of treated leaves showed few significant differences due to treatment during the water stress period.

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John Erwin, Tanveer Hussein, and David J. Baumler

temperatures for pepper photosynthesis range from 25 to 35 °C, and temperatures outside this range can limit the yield; for example, C . chinense flower abortion increased 2-fold and fruit set decreased 3-fold when greenhouse temperatures were increased from