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Svoboda V. Pennisi and Marc W. van Iersel

) quantify the amount of carbon assimilation in situ in a commercial interiorscape composed of a variety of plant species and sizes. Materials and Methods Simulated environment Plant material. The study extended over a period of 16 months, from Feb. 2009 to

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D. Michael Glenn, Amnon Erez, Gary J. Puterka, and Patricia Gundrum

Processed-kaolin particle films (PKPFs) are used commercially in large quantities on horticultural crops to repel insects, and reduce heat stress and solar injury of fruit. Our studies determined the effect of two processed-mineral particle film materials (kaolin and calcium carbonate), on whole plant carbon assimilation, water use efficiency, yield, mean fruit weight and quality in `Empire' apple [(Malus ×sylvestris (L.) Mill var. domestica (Borkh Mansf.))] over a four-year period. The application of a PKPF reduced canopy temperature, and probably reduced environmental stress, resulting in increased mean fruit weight and red color in two of the four years of the study. Whole canopy carbon assimilation studies indicated increased carbon assimilation only under conditions of high air temperature. The PKPF sprayed leaves also had reduced water use efficiency; likely due to increased stomatal conductance associated with reduced leaf temperature. Calcium carbonate had none of the positive effects of PKPF and reflected more photosynthetically active radiation (PAR) than the PKPF.

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Yaffa L. Grossman and Theodore M. DeJong

Plant dry matter production is proportional to light interception, but fruit production does not always increase with increased light interception. Seasonal daily patterns of light interception by cling peach trees planted in four different planting density/training systems were obtained using a Decagon ceptometer. The High Density V system (1196 trees/ha) intercepted significantly more light than the KAC V and Cordon systems (918 trees/ha). The Vase system (299 trees/ha) intercepted significantly less light than the other systems. Response surfaces using a quadratic model with interactions for time of day and day of year explained 84% to 91% of the variance in the data sets for each training system. Crop yields per acre were greatest for the High Density V, followed by KAC V, Cordon, and Vase, corresponding to the light interception data. A carbon budget model, which incorporated canopy photosynthesis, respiration, and carbon partitioning based on organ growth potentials, was used to simulate seasonal patterns of carbon assimilation, crop dry weights, and individual fruit dry weights.

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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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Christopher Ramcharan, Dewayne L. Ingram, Terril A. Nell, and James E. Barrett

Short-term effects of root-zone temperatures (RZT) of 28, 33, 38, and 43C for 6 hours daily on container-grown Musa spp. (AAA) `Grande Naine' and Ixora chinensis L. `Maui' were determined under greenhouse and growth room conditions. Diurnal fluctuation of leaf carbon assimilation (LCA) was altered by treatments. In the growth room at 43C, the maximum LCA occurred about midday for banana, but not until afternoon in ixora. LCA was highest (0.53 mg CO2/m2 per sec) in banana with a 33C RZT under greenhouse conditions, while it was equally high (0.74 mg CO2/m2 per sec) at 33 and 38C in a growth room. In ixora, 33C induced the highest LCA (0.40 mg CO2/m2 per sec) in the greenhouse at 1200 hr, but there were no apparent differences in midday LCA between plants with RZT of 28, 33, and 38C in the growth room. Effects of RZT and environment on the daily fluctuations of gaseous exchange processes raise questions about using measurements at only one time during the day to separate treatment effects.

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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.

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Lingyun Yuan, Yujie Yuan, Shan Liu, Jie Wang, Shidong Zhu, Guohu Chen, Jinfeng Hou, and Chenggang Wang

High temperature (HT) is a major environmental stress limiting oversummer production of nonheading Chinese cabbage (NHCC, Brassica campestris ssp. chinensis Makino). In the present study, the effects of HT on photosynthetic capacity, including light reaction and carbon assimilation, were completely investigated in two NHCC, ‘xd’ (heat-tolerant), and ‘sym’ (heat-susceptible). The two genotypes showed significant differences in plant morphology, photosynthetic capacity, and photosynthate metabolism (carboassimilation). HT caused a decrease in photosynthesis, chlorophyll contents, and photochemical activity in NHCC. However, these main photosynthetic-related parameters, including net photosynthetic rate (PN), maximal photochemical efficiency of PSII (Fv/Fm), and total chlorophyll content in ‘xd’, were significantly higher than those of ‘sym’ plants. The antioxidant contents and antioxidative enzyme activities of ascorbic acid-reduced glutathione cycle in the chloroplast of ‘xd’ were significantly higher than those of ‘sym’. Microscopic analyses revealed that HT affected the structure of photosynthetic apparatus and membrane integrity to a different extent, whereas ‘xd’ could maintain a better integrated chloroplast shape and thylakoid. Inhibited light reaction also hampered carbon assimilation, resulting in a decline of carboxylation efficiency and imbalance of carbohydrate metabolism. However, larger declined extents in these data were presented in ‘sym’ (heat-susceptible) than ‘xd’ (heat-tolerant). The heat-tolerant genotype ‘xd’ had a better capacity for self-protection by improved light reaction and carbon assimilation responding to HT stress.

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Renée L. Eriksen, Laban K. Rutto, James E. Dombrowski, and John A. Henning

photosystems themselves, particularly photosystem II (PSII); the ATP-generating electron transport chain; and the carbon assimilation process. Heat affects the photosystems by causing the dissociation of manganese (Mn) molecules from the oxygen-evolving complex

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Chris A. Martin, Sean A. Whitcomb, and Jean C. Stutz

of soil sampled. Total percent root colonization was multiplied by the RLD to determine the length of root colonized per cubed centimeter of soil. During February and June 2001, measurements of leaf carbon assimilation (A) and conductance ( g s

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Abdul K. Janoudi and Irvin E. Widders

The effects of water deficit and fruiting on leaf gas exchange and dry-matter production and partitioning in cucumber (Cucumis sativus L.) plants were evaluated in greenhouse and field experiments. Fruiting plants had higher photosynthetic rates (15.8 μmol·m-2·s-1) than defruited plants (12.7 μmol·m-2·s-1). Although stomatal conductance was lower in defruited plants, it accounted for only ≈35% of the assimilation rate (A) reduction. Under water deficit, defruiting caused a similar response in A, even though A was only ≈50% of that in watered plants. Fruiting and water deficits limited vegetative plant dry weight and total leaf area. In field experiments, removing flowers from the first four or eight nodes resulted in a higher count and fresh weight at harvest of only those pickling cucumber fruit that were irrigated.