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Noreen S. Khoury and E. Jay Holcomb

Greenhouse substrates are designed to allow maximum aeration. Substrate water holding capacity can be increased by media compaction.

Six inch standard pots, fitted with gas tight openings for removing gas samples, were filled with Metromix 350 and Peatwool at 2 different compaction rates. Half the pots were planted with rooted cuttings of Poinsettia pulcherrima `Glory' and half were left fallow. Air samples were taken at both wet and dry soil moisture conditions at early, mid point and at the end of the cropping cycle. In general, wet substrates had higher CO2 than drier substrates and more compacted substrates had higher CO2 than less compacted.

CO2 decreased with time in all treatments. The highest CO2 levels occurred in wet heavily compacted Peatwool with a plant and the lowest occurred in dry Metromix with no plant.

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R.J. Bender and J.K. Brecht

Mangoes for long-distance markets are harvested at the mature-green stage and shipped in refrigerated containers. Shipment under controlled atmosphere is still tentative, and the CO2 concentrations used are relatively low (maximum 10%), although mangoes have been reported as being less-sensitive to elevated CO2 than other tropical fruits. In the present study, CO2 concentrations of 10%, 15%, 25%, 35%, and 45% combined with 5% O2 were used to store mangoes. Mature-green `Tommy Atkins' were stored for 21 days at 12C, followed by air storage at 20C for 5 days. Tree-ripe mangoes were stored at 8 or 12C under the same conditions. Ethanol production rates increased along with increasing CO2 concentrations. However, only 35% and 45% CO2 atmospheres inflicted damage. Color development was severely inhibited under those treatments. Lower CO2 treatments, up to 25% in the storage atmosphere, inhibited skin color development and ethylene biosynthesis but, after 5 days in air at 20C, skin color and ethylene production reached control levels. Fruit flesh firmness did not differ among treatments at 12C. Tree ripe mangoes stored in CA at 8C were only significantly firmer than control fruit at transfer from CA to air.

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Sang Deok Lee, Soon Jae Kim, Seung Il Jung, Ki-Cheol Son, and Stanley J. Kays

CO2 assimilation rate of Crassula hybrid `Himaturi', a succulent ornamental species with the crassulacean acid metabolism (CAM) photosynthetic pathway, was affected by light intensity (50, 100, 300 μmol·m–2·s–1), photoperiod (16/8, 8/16 h day/night), and temperature (30/25, 25/20 °C day/night). Maximum assimilation of CO2 occurred at 300 μmol·m–2·s–1 of diurnal irradiance, 16/8 h day/night photoperiod, and a day/night temperature of 30/25 °C. Diurnal CO2 assimilation patterns of nine succulent ornamental CAM species were evaluated (300 μmol·m–2 s–1, 35/25 °C day/night and a 16/8-h day/night photoperiod) for CO2 fixation. Of the nine ornamentals, Crassula `Himaturi' had the highest and Echeveria derembergii the lowest maximum CO2 absorption rate (13.0 vs 2.4 μmol kg–1·s–1), total nighttime (179.3 vs 13.4 mmol·kg–1), and 24 h total (200.6 vs 19.0 mmol·kg–1) absorption. Based on the CO2 assimilation patterns, the nine ornamentals were separated into two groups: 1) full CAM (Faucaria tigrina, Gasteria gracilis var. minima, Haworthia cymbiformis, and Haworthia fasciata); and 2) weakly CAM (Adromischus clarifolius, Crassula hybrids `Moonglow' and `Himaturi', E. derembergii, and Haworthia retusa).

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Brent Tisserat and Robert Silman

An inexpensive ultrasonic fogging system is presented that aids in the establishment of tissue culture shoots in soil under greenhouse conditions. In addition, ultrasonic fogging may be coupled to CO2 nutrient enhancement via bubbling CO2 into the water reservoirs prior to fogging to improve growth and morphogenesis responses of shoots. A list and cost of items for the system and its assembly is given. Transplanted tissue culture shoots of basil (Ocimum basilicum L.), hosta (Hosta sp.), mint (Mentha sp.), and thyme (Thymus vulgaris L.) were tested with this fogging system with and without CO2 nutrient elevation and compared to the growth of shoots grown under a misting system with and without CO2 nutrient elevation. In all cases, ultrasonic fogging enhanced survival rates, growth (fresh weights) and morphogenesis (axially shoots, leaves and roots) vs. that occurring in the misting system. For example, thyme and mint shoots exhibited 2- and 5-fold increases, respectively, in fresh weights under ultrasonic fogging with CO2 compared to misting systems with CO2. Associated with enhanced survival and morphogenesis was an overall enhancement of shoot and leaf size and overall maturation responses. This is also reflected in enhanced secondary products obtained from shoots grown under ultrasonic fogging compared to shoots grown in misting systems.

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R.C. Beeson Jr and M.E.D. Graham

The effect of prolonged CO2 enrichment on the activities of ribulose l,5-bisphosphate carboxylase/oxygenase (Rubisco) and carbonic anhydrase (CA) of greenhouse roses were studied. Plants of Rosa × hybrids `Red Success' were grown for 2 years at ambient and 900 μl CO2/liter during winter and spring with 75 μmol·m-2·s-1 photosynthetically active radiation supplemental lighting for 2 years. Measurements of initial and Mg+2-CO2-activated activities of Rubisco and CA were made during shoot development and at different positions within the plant canopy. Generally, there were no significant differences measured in the enzyme activities between the two CO2 concentrations. The results suggest that the photosynthetic capacity did not change and that there were no characteristic adaptations to long-term growth (up to 20 weeks) at elevated CO2 concentrations. The maintenance of Rubisco and CA activities with prolonged exposure to CO2-enriched atmospheres is proposed as the reason for long-term yield increases in roses when grown in enriched environments.

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Ian R. Rodriguez, Lambert B. McCarty, Joe E. Toler, and Roy B. Dodd

Use of creeping bentgrass [Agrostis stoloniferous L. var. palustris (Huds.)] on golf greens has expanded into the hotter, more humid regions of the United States where its quality is often low during summer months. The summer decline in bentgrass quality may be partially attributed to respiration rates exceeding photosynthesis during periods of supraoptimal temperatures and adverse soil conditions, such as excessive CO2 and inadequate O2 levels. The objectives of this study were to examine the effects of high temperature, high soil CO2, and irrigation scheduling on creeping bentgrass growth. A growth chamber study was conducted using `A-1' creeping bentgrass. Treatments included all combinations of three day/night temperature regimes (26.5/21 °C, 29.5/24 °C, and 32/26.5 °C), three irrigation schedules (field capacity daily, field capacity every two d, and half field capacity daily), and four soil CO2 injection levels (10%, 5%, 0.03%, and a noinjection control). Creeping bentgrass shoot and root dry weights and net photosynthetic rates were greater for day/night temperatures <32/26.5 °C. High temperatures (32/26.5 °C) and 10% CO2 reduced bentgrass net photosynthesis by 37.5 μmol CO2/m2/s. Shoot and root total nonstructural carbohydrates also were lowest for highest temperature regime. Respiration exceeded gross photosynthesis at 32/26.5 °C when 5% and 10% CO2 injection levels were used, indicating a carbon deficit occurred for these conditions. Irrigation volume and frequency did not affect bentgrass growth. High temperatures combined with high soil CO2 levels produced poorest turf quality.

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Kenneth W. Mudge, Joseph P. Lardner, and Katherine L. Eckenrode

The objective of this study was to determine the feasibility of CO2 enrichment and optimal radiation level for accelerating the rooting and growth of micropropagated Kalmia latifolia cuttings during the Stage IV acclimation period. Inch long microcuttings of the Kalmia cultivars `Elf' and `Carousel' shipped from a commercial micropropagation laboratory, were stuck in flats of peat, and place in a fogging chamber constructed to allow for the simultaneous experimental variation of CO2 level and either radiation level or photoperiod. Treatments consisted of a complete factorial arrangement of 2 levels of CO2 (ambient and 1200 ppm) and 3 levels of radiation (30, 98, and 158 μmoles/m2/sec). The experiment was repeated 6 times. For `Carousel' CO2 enrichment stimulated both shoot and root growth and either the high or medium light level was optimal depending on the experiment. CO2 enrichment also stimulated growth of `Elf' but results were less consistent from experiment to experiment. Similar experiments are in progress with Amelanchier and Lilac microcuttings.

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R.E. Moran, D.E. Deyton, C.E. Sams, J. Cummins, and C.D. Pless

Soybean oil can be used as an alternative pesticide for fruit trees. Two separate studies were conducted to determine the effects of oil concentration on leaf phytotoxicity and net CO2 assimilation (ACO2). In one study, concentrations of 0%, 2%, 4%, and 6% soybean oil in water were applied to individual shoots with a hand-held mist bottle. In the second study, 0%, 1.0%, and 1.5% were applied to whole trees with an airblast sprayer. Petroleum oil was applied as a separate treatment. Net CO2 assimilation was measured on single leaves. Oil residue was removed from the leaf with chloroform, dried, and weighed. Chlorosis and defoliation occurred with applications of 4% and 6% soybean oil. No visible phytotoxicity occurred with 2% or less oil. Net CO2 assimilation decreased as the rate of soybean oil increased from 0% to 4% oil, but there was no difference between 4% and 6%. Net CO2 assimilation decreased with increasing oil concentration from 0% to 1.5% and recovered to the rate of the control on day 7. Net CO2 assimilation was negatively related to oil residue. At an equivalent oil residue, there was no difference in ACO2 between petroleum and soybean oil. Below a residue of 0.15 mg·cm–2, foliar phytoxicity did not occur. Reductions in ACO2 were small and did not last longer than 7 days if residues were ≤0.10 mg·cm–2.

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Theophanes Solomos and John C. Bouwkamp

Previous observations have shown that the diffusivity of water vapors is much larger than the value that is predicted theoretically from the magnitude of the diffusion coefficient of CO2, C2H4, or both. This has been ascribed to the ability of water to diffuse through the cuticle and to the transport of water via the capillaries of cellulase micorfibrels to the surface of the lenticels, where it evaporates. We measured the diffusivity of CO2 in `Gala' and `Granny Smith' apples. The former are more permeable to CO2 than the latter cultivar, in particular after prolonged storage at 2°C. The diffusivity of H2O was 10- to 20-fold larger than that of CO2. Furthermore, the ratio of D(H2O)/D(CO2) was similar for both cultivars. Infiltration of dyes and gas flow through apples submerged in water show that in `Gala' apples, the number of open lenticels is larger than in `Granny Smith'. Thus, the data indicate that lenticels are the main avenue of gas exchange in apples.

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Mengmeng Gu, Curt R. Rom, James A. Robbins, and Hyun-Sug Choi

The genus Betula consists of approximately 50 deciduous species throughout northern hemisphere. Net CO2 assimilation ([A]) of four birch taxa (Betula alleghaniensis Britton, B. davurica Pall., B. nigra L. `Heritage', and B. papyrifera Marsh.) was measured with a portable gas exchange system, CIRAS-I. Light was increased from 0 to 2000 μmol· m-2·s-1 at increments of 25, 50, 100, 250, 500, 750, 1000, 1250, 1500, 1750, 2000 μmol·m–2·s–1 to create an [A] light-response curve. CO2 concentration was gradually increased to 1100 ppm in increments 50, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000, 1100 ppm to create an [A]-Ca (ambient CO2) curve. B. davurica had significantly higher potential A capacity than the other taxa under high CO2 conditions. Betula nigra `Heritage' had the highest carboxylation efficiency among four taxa. B. davurica and B. nigra `Heritage', had higher [A] when ambient CO2 is 0ppm. Betula davurica and B. nigra `Heritage', had higher light-saturated rate of gross [A] than B. alleghaniensis and B. papyrifera.