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John Erwin and Esther Gesick

concentration at 95% of P max approximated the CO 2 saturation point (CSP; CO 2 when P n was saturated). Experimental design and data analysis. Analysis of variance (ANOVA) was conducted on photosynthetic parameters derived from Eqs. [1] and [2] fit to

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William R. Nail and G. Stanley Howell

Potted grapevines (Vitis vinifera L. `Chardonnay') were inoculated with conidial suspensions of the grapevine pathogen causing powdery mildew of grape (GPM) (Uncinula necator (Schw.) Burr.). Leaves of inoculated and noninoculated vines were studied for the effects of varying light (PAR) and CO2 concentrations on factors affecting carbon assimilation. GPM reduced carboxylation efficiency (k), net CO2 assimilation rate (A), stomatal conductance (g s), and internal CO2 concentration (Ci) under ambient CO2, A max at >900 ppm CO2, stomatal limitations to A (lg), and photochemical efficiency (Φ) on diseased leaves, while having no effect on the CO2 compensation point (Γ) or the light compensation point (cp). GPM had no significant effect on chlorophyll fluorescence (Fv/Fm).

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Jan M. Kossowski and David W. Wolfe

Long- and short-term physiological responses of pak choi (Chinese cabbage, Brassica campestris cv. `Hypro') to elevated CO2 and light environments were evaluated in the series of growth chamber experiments. Plants were grown hydroponically (Nutrient Film Technique) at 25/18°C (day/night) temperature, a 16-h photoperiod, and at three CO2 levels (350, 700, 1400 ppm) and two light levels (200 and 400 μmol·m–2·s–1 PPFD). Relative to 350-ppm CO2 treatment, the final total plant dry mass in low light increased by 37% and 38% at 700 and 1400 ppm CO2, respectively. In high light the increase was 7% and 13% at 700 and 1400 ppm CO2, respectively. Light response curves showed a positive CO2 effect on light compensation point, a slight increase in quantum yield and increase in maximum Pn rates at elevated CO2. Carbon dioxide response curves (measured at saturating PPFD of 1600 μmol·m–2·s–1) showed no effect of growth light treatment on the CO2 compensation point, but a 20% to 30% higher maximum Pn rate at saturating CO2 in plants grown at the higher light level. Overall, the highest Pn rates and the highest plant dry mass at final harvest were found in plants grown at the 400 μmol·m–2·s–1 PPFD and 1400 ppm CO2. Relative beneficial CO2 effects, however, were the most pronounced in low light conditions.

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Tim D. Davis and John R. Potter

Abstract

Root formation on leafy cuttings of Pisum sativum L. ‘Alaska’ was reduced by about 50% when net photosynthesis was adjusted to the compensation point by reducing the light intensity, reducing the CO2 concentration, or by blocking CO2 exchange with an antitranspirant. Rooting was also reduced by 50% when cuttings were given only enough photoperiod at saturating light to maintain a carbon balance similar to that of the treatments which reduced net photosynthesis to the compensation point. In addition to decreasing rooting, these treatments lowered sucrose and glucose levels in the basal portion of the cuttings compared to controls. Our photosynthesis and carbohydrate data indicate that the supply of current photosynthate to the base of pea cuttings is important to rooting.

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Gang-Yi Wu, Jun-Ai Hui, Zai-Hua Wang, Jie Li, and Qing-Sheng Ye

CE of RuBPCase. The P n at the CO 2 light saturation point was the regenerating rate of RuBP. Temperature response curve. The P n value of each temperature gradient within the range of 18 to 34 °C was measured from low to high temperature using the

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Jeffrey A. Leshuk and Mikal E. Saltveit Jr.

A method is described for the rapid determination of the anaerobic compensation point (ACP) of plant tissue, i.e., the O2 concentration at which CO2 production is minimum. The rate of CO2 production is measured from tissue exposed to an exponentially declining O2 concentration produced by a flow of N2 into a dilution bottle initially containing air. Too rapid a rate of O2 decline produces abnormal data because of the time required for the tissue to respond to changes in O2 concentration. The ACP is easily determined from a plot of CO2 production vs. O2 concentration. Rates of CO2 production and ACPS calculated using the exponentially declining system are similar to those calculated from traditional methods of continuously holding tissue under various O2 concentrations.

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K.A. Corey, R.M. Wheeler, J.C. Sager, and R.P. Prince

A wheat (Triticum aestivum cv. Yecora Rojo) stand was grown using nutrient film culture in the closed conditions of NASA's Biomass Production Chamber. Rates of photosynthesis and respiration of the entire stand (about 20 m2) were determined daily using a regime of 20 hr light/4 hr dark, 20 C light/16 C dark an average PPF of 600 μmol/m2/s from HPS lamps, and a CO2 cone of 1000 ppm. Fractional interception of PPF by the stand reached a maximum of 0.96 at 24 days from planting. Rates of photosynthesis were constant throughout the photoperiod as determined by short term drawdowns of CO2 throughout the photoperiod. Drawdown rates of CO2 were correlated with rates determined by logging of mass flow of CO2 injected during chamber closure. Photosynthetic drawdowns of CO2 indicated that photosynthesis was not saturated at 1000 ppm CO2 and that the CO2 compensation point was about 50 ppm. Whole stand light compensation points were 200 to 250 μmol/m2/s between days 13 and 70 and then increased rapidly during senescence.

Open access

C. E. Sams and J. A. Flore

Abstract

Net photosynthetic rate (Pn) of leaves of sour cherry (Prunus cerasus L. cv. Montmorency) was greater for leaves between nodes 9 and 13 than for either older, mature leaves or newly expanding leaves on the same shoot. For individual leaves, Pn reached maximum when the leaf was greater than 80% expanded, remained constant for 2 to 4 weeks, then gradually declined. Hyperbolic and parabolic response curves were observed in response to light and temperature, respectively. Maximum Pn occurred at light intensities between 800–1200 μEm−2s−1. Optimum temperature ranged with light level and vapor pressure deficit (YPD), but was generally between 15 to 30°C. Pn increased as CO2 concentration increased between 0 and 600 ppm, the CO2 compensation point being about 80 ppm. Under optimum conditions Pn ranged between 30 to 35 mg CO2 dm−2 hr−1.

Open access

A. Bar-Tsur, J. Rudich, and B. Bravdo

Abstract

The effect of temperature on CO2 fixation was studied in 2 tomato (Lycopersicon esculentum Mill.) cultivars; the heat-sensitive “Roma VF” and the heat-tolerant “Saladette". A decrease in apparent photosynthesis was found in both cultivars after plant exposure for various lengths of time to temperatures of 35° to 40°C. An increase in temperature also increased transpiration and raised the CO2 compensation point. The decrease in photosynthesis after a short exposure to high temperature was due to an increase in mesophyll resistance and, to a lesser extent, to an increase in stomatal resistance to CO2 diffusion. Saladette was less affected by high temperature and had a slightly greater photosynthetic capacity than the heat-sensitive Roma VF, after pretreatment at high temperature.

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Gary W. Stutte, Neil C. Yorio, and Raymond M. Wheeler

The effect of photoperiod (PP) on net carbon assimilation rate (Anet) and starch accumulation in newly mature canopy leaves of `Norland' potato (Solanum tuberosum L.) was determined under high (412 ∝mol·m-2·s-1) and low (263 ∝mol·m-2·s-1) photosynthetic photon flux (PPF) conditions. The Anet decreased from 13.9 to 11.6 and 9.3 μmol·m-2·s-1, and leaf starch increased from 70 to 129 and 118 mg·g-1 drymass (DM) as photoperiod (PP) was increased from 12/12 to 18/6, and 24/0, respectively. Longer PP had a greater effect with high PPF conditions than with low PPF treatments, with high PPF showing greater decline in Anet. Photoperiod did not affect either the CO2 compensation point (50 μmol·mol-1) or CO2 saturation point (1100-1200 μmol·mol-1) for Anet. These results show an apparent limit to the amount of starch that can be stored (≈15% DM) in potato leaves. An apparent feedback mechanism exists for regulating Anet under high PPF, high CO2, and long PP, but there was no correlation between Anet and starch concentration in individual leaves. This suggests that maximum Anet cannot be sustained with elevated CO2 conditions under long PP (≥12 hours) and high PPF conditions. If a physiological limit exists for the fixation and transport of carbon, then increasing photoperiod and light intensity under high CO2 conditions is not the most appropriate means to maximize the yield of potatoes.