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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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Sara Andrea Moran-Duran, Robert Paul Flynn, Richard Heerema, and Dawn VanLeeuwen

time × N × Ni ( P = 0.0403). Because of the two, three-way interactions involving all factors, significant means for tree group, time, N, and Ni combinations are reported in Table 3 . Table 3. Least square (LS) means for net photosynthesis (μmol·m −2

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Richard P. Marini and Donald L. Sowers

`Redhaven' peach [Prunus persica (L.) Batsch] trees were shaded to five light levels [100%, 45%, 23%, 17%, and 9% photosynthetic photon flux (PPF)] for four different periods. Net photosynthesis (Pn), measured under the various shade levels, increased nonlinearly with increasing percent PPF. After 18 days of shading, specific leaf weight (SLW) was positively and linearly related to percent PPF. After shade removal, Pn and SLW returned to control levels in 26 and 4 days, respectively. Flower density was positively related to percent PPF when trees were shaded from 16 June to 4 July or 4-31 July, but not from 31 July to 30 Sept. of the previous year.

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S.E. Garrison, J.M. Williams, and J.A. Barden

A greenhouse experiment was conducted to determine the effects of shade treatments (0, 30, 47 and 63%) on photosynthetic and growth responses of `Redchief' strawberries. Net photosynthesis (Pn) measured on plants under shade decreased as % shade increased. Pn of plants grown under shade but measured under saturating light intensities decreased after 30% shade. Light saturation curves of leaves allowed to expand in full sun and then placed under shade indicated a decrease in the saturation rate and point under 63% shade. Leaves which expanded under shade had decreased saturation rates and points at all levels. Specific leaf weight and total plant dry weight decreased linearly as % shade increased.

A field study in which plants were either shaded in the fall or in the fall and spring demonstrated a decreasing trend in berry number for plots which were shaded in the fall and spring. Berry number decreased in fall-shaded plants after 30% shade. In both cases, berry weight decreased with increasing shade.

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

Gas exchange (net photosynthesis Pn, dark respiration, transpiration, and stomatal resistance) of `Jaqueline' Alstroemeria, grown in pots in a greenhouse, were measured. Measurements were made under laboratory conditions using an open-flow infrared gas analysis system for leaf studies, and a semi-closed computer controlled whole plant photosynthesis system for whole plant studies.

Apical fully expanded leaves on non-flowering and flowering (at two stages) shoots had similar photosynthetic responses in respect to photosynthetically active radiation (PAR) and to CO2 concentration. Light saturation occurred at 600 umol/m2/s PAR with maximum leaf Pn rates ranging from 9 to 11 umol CO2/m2/s. CO2 saturation was estimated at approximately 1100 to 1200 ppm with maximum leaf Pn rates from 17 to 22 umol CO2/m2/s.

Whole plant Pn rates increased with increased PAR. Maximum rates 4 to 5 umol CO2/m2/s (half that of individual leaves) occurred at approximately 1000 to 1100 umol/m2/s PAR. CO2 saturation was estimated at 1100 to 1200 ppm, with maximum whole plant Pn rates ranging from 7 to 8 umol CO2/m2/s. These data will be discussed in relation to respiration and mutual shading at the leaf canopy.

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J.H. Lieth and C.C. Pasian

A mathematical description for the relationship between the rate of rose (Rosa hybrida L.) leaf net photosynthesis and photosynthetically active radiation, leaf temperature, and leaf age is developed. The model provides a tool for the prediction of these rates for leaves growing in a rose crop canopy.

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Carl-Otto Ottosen

Abbreviations: C I , internal CO 2 concentration (ppm CO 2 ); G 5 , stomatal conductance (mol·s -1 ·m -2 ); P N , net photosynthetic rate (μmol CO 2 /sec per square meter); T, transpiration rate (μmol H 2 O/sec per square meter). 1 Former Research

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D.P. Miller, G.S. Howell, and J.A. Flore

Chambers were constructed to measure gas exchange of entire potted grapevines (Vitis vinifera L.). The plant enclosures were constructed from Mylar film, which is nearly transparent to photosynthetically active radiation. Maintaining a slight, positive, internal pressure allowed the Mylar chambers to inflate like balloons and required no other means of support. The whole-plant, gas-exchange chamber design and construction were simple and inexpensive. They were assembled easily, equilibrated quickly, and did not require cooling. They allowed for the measurement of many plants in a relatively short period. This system would enable the researcher to make replicated comparisons of treatment influences on whole-plant CO2 assimilation throughout the growing season. While CO2 measurement was the focus of this project, it would be possible to measure whole-plant transpiration with this system.

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Hening Hu and Darrell Sparks

Seedlings of pecan [Carya illinoensis (Wangenh.) C. Koch] grown in perlite culture were treated with N and S in a 5 × 5 factorial in a randomized complete block design to determine the effect of N, S, and N × S interaction on vegetative growth and photosynthesis. Nitrogen and S deficiency symptoms occurred when leaf N and S were < 25 and 1.4 mg·g-1 dry weight, respectively. Photosynthesis was reduced when combined leaf N and S exceeded 35 and 3.7 mg·g-1 dry weight, respectively; growth was reduced when leaf N and S were > 34 and 3.7 mg·g-1 dry weight, respectively. Photosynthesis and growth increased with N supply, but depended on leaf N: S ratio. In plants without visible N or S deficiency, a N: S ratio of ≈9. is proposed to be near the optimum for maximum growth. Comparison of leaf N, S, and the N: S ratio with similar analyses in selected orchards suggests that pecan productivity will increase from S application under field conditions. We conclude that the interaction” of N and S imposes stringent controls on leaf N and S, photosynthesis, and growth.

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Yao-Chien Chang, Hsiao-Wei Chen, and Nean Lee

Photosynthetic rate is reduced during midday in some crops; this phenomenon has been termed as midday depression (MD). Oncidium also suffers greatly from MD in the summer, resulting in reduced growth and poor flowering quality. Since high radiation usually accompanies high temperature midday in the summer, it is difficult to figure out the key factor that promotes MD. We investigated the photosynthetic activities of Oncidium Gower Ramsey in the following conditions: environment-controlled and nonenvironment-controlled. In a growth chamber that simulated field growth conditions, photosynthesis declined dramatically when the temperature was higher than 32 °C. Photosynthesis was also reduced when photosynthetically active radiation (PAR) exceeded the saturating point of Oncidium. Gower Ramsey, which is about 250 μmol·m-2·s-1. However, the reduction was slight when PAR was under 500 μmol·m-2·s-1. Daily photosynthetic patterns were changed when Oncidium Gower Ramsey was grown under different environments. By regression, we found that MD was not directly associated with PAR within the range of 0–400 μmol·m-2·s-1. By contrast, photosynthesis was significantly reduced when temperature was higher than 32 °C. This explains the observation of greater photosynthetic reduction and earlier occurrence of MD when Oncidium Gower Ramsey was grown in rain-shelter rather than in phytotron and growth chamber, since temperature in the rain-shelter was not controlled, while the others were controlled at 25 °C. When Oncidium Gower Ramsey was moved from 35 °C to 25 °C, the photosynthetic depression was relieved.