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Marc van Iersel

Salvia splendens `Top burgundy' was grown in pots of different sizes (5, 50, 150, and 450 mL) to assess the effect of rooting volume on the growth and development of salvia. Seeds were planted in a peat-lite growing medium and plants grown in a greenhouse during the winter and spring of 1996. Plants were spaced far enough apart to minimize mutual shading and interplant light competition. Plants were harvested at weekly intervals and shoot and root dry mass and leaf area were measured. Relative growth rate (RGR) and net assimilation rate were calculated from these data. Differences in plant size became evident at 25 days after seeding. A small pot size (5 mL) decreased root and shoot dry mass, RGR, and NAR, while increasing the root:shoot ratio. Differences between the pot sizes became more apparent during the course of the experiment. The observation that root: shoot ratio decreased with increasing pot volume suggests that the decreased plant size in smaller pots was not the direct effect of reduced root size. Growth most likely was limited by the ability of the roots to supply the shoots with sufficient water and/or nutrients. Pot volume did not only affect the growth, but also the development of the plants. Salvia flowered faster in bigger pots (about 50 days after seeding in 450-mL pots), while the plants in 5-mL cells did not flower during the 9-week period of the experiment.

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Douglas D. Archbold and Ann M. Clements

Several components of whole-plant growth were compared among accessions of Fragaria chiloensis (FC) and F. virginiana (FV) grown at 23 and 31 °C daytime temperatures. The accessions loosely represented North American (NA) and South American (SA) provenances of FC and Kentucky (KY) and eastern Canadian (CN) provenances of FV. Differences in component values between species and by provenance and accession within species were observed at each temperature. Using the ratio of the component value at 31 °C to that at 23 °C as a basis for comparisons, whole-plant relative growth rate (RGR), leaf net assimilation rate (NAR), root RGR, and root: shoot ratio were reduced relatively more by high temperature in FC than FV, while crown RGR, leaf RGR, and leaves produced per day were not consistently affected by temperature or and did not differed significantly between species. While the SA FC exhibited higher values for nearly all components than the NA FC at both temperatures, both were affected similarly by high temperature. The CN FV exhibited somewhat greater sensitivity to high temperature than the KY FV, with significantly lower leaf NAR, crown RGR, and leaves produced per day in the former group.

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Nader Soltani, J. LaMar Anderson, and Alvin R. Hamson

`Crimson Sweet' watermelon [Citrullus lanatus (Thunb.) Matsum. & Nakai] plants were grown with various mulches and rowcovers and analyzed for relative growth rate (RGR), net assimilation rate (NAR), specific leaf area (SLA), leaf area index (LAI), and crop growth rate (CGR). Spunbonded polyester fabric (SB-PF) and perforated polyethylene film (PCP) rowcovers generally showed greater mean RGR, SLA and CGR than spunbonded polypropylene polyamide net (SB-PP), black plus clear combination plastic mulch and black plastic mulch alone. Plants on mulches and under rowcovers showed significant increases in RGR, NAR, and SLA over plants grown in bare soil. Carbon dioxide concentration inside the transplanting mulch holes was nearly twice the ambient CO, concentration. Growth analysis of sampled watermelon plants during early stages of development under various treatments was predictive of crop yield. Plants under SB-PF and PCP rowcovers produced the earliest fruit and the greatest total yield. An asymmetrical curvilinear model for watermelon growth and development based on cardinal temperatures was developed. The model uses hourly averaged temperatures to predict growth and phenological development of `Crimson Sweet' watermelon plants grown with and without rowcovers. Early vegetative growth correlated well with accumulated heat units. Results indicate a consistent heat unit requirement for the `Crimson Sweet' watermelon plants to reach first male flower, first female flower and first harvest in uncovered plants and plants under rowcovers. Greater variability was observed in predicting date of first harvest than first bloom.

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Bruce W. Wood and William R. Joyner

Observations of net assimilation rates (`A') by pecan sun and shade leaves in relation to various levels of solar irradiation, the light adaptation characteristics of these leaf types, the role of clouds in suppressing the penetration of solar irradiation, and the abundance of cloud cover in the southeastern U.S. during the growing season, suggest that nut production throughout the U.S. pecan belt is being limited by insufficient sunlight with the southeastern U.S. (comprising about 2/3 of the commercial U.S. pecan production) being especially impacted. In support of this hypothesis, regression analysis showed cultivar-type nut production for Georgia from 1977-1989 to be significantly (P<.0001, R2 = 0.79) associated with sunlight levels ≥ 3000 Wh m-2d-1 from mid August to early October for the same year. This is taken as evidence that the amount of sunlight reaching the canopy seems to be a major factor that should be considered in relation to orchard site selection and canopy management techniques.

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Kyle R. Mankin and R. Peter Fynn

Nutrient uptake by New Guinea impatiens (Impatiens X hb.) `Equinox' was measured in a growth chamber under various combinations of light [photosynthetic photon flux (PPF)], air temperature, and nutrient solution concentration. Nitrate-N, P, K, Ca, and Mg ions were evaluated individually by measuring depletion of each nutrient from a constant-volume solution over 9 hours with constant environmental conditions. Individual nutrient uptake was not correlated to concurrent daily temperature environment, and only K and Mg showed a correlation with PPF. Uptake rates of N, P, K, Ca, and Mg increased significantly with increasing nutrient solution concentration. Estimated net assimilation rates of nutrients, based on measured shoot tissue concentrations of each nutrient and assuming that uptake occurred continuously at a rate proportional to canopy area, were correlated to average measured uptake rates for N, Ca, and Mg and were not correlated to average uptake rates for P and K. Although nutrient demand from plant growth may determine rates of nutrient uptake necessary over longer periods of time, short-term uptake was not related directly to daily fluctuations in environmental factors.

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Gina E. Fernandez and Marvin P. Pritts

Seasonal changes in growth, mean maximal photosynthetic rates, and the temperature and light response curves of `Titan' red raspberry (Rubus idaeus L.) were obtained from potted plants grown under field conditions. Primocane dry weight accumulation increased steadily at the beginning and the end of the season, but growth slowed midseason during fruiting. The slower midseason dry-weight accumulation rate coincided with an increase in root dry weight. Primocane net assimilation rate (NAR) was highest early in the season. Floricane photosynthetic rates (A) were highest during the fruiting period, while primocane A remained steady throughout the season. Primocane and floricane leaflets displayed a midday depression in A under field conditions, with a partial recovery in the late afternoon. Photosynthetic rates of primocane and floricane leaves were very sensitive to temperature, exhibiting a decline from 15 to 40C. Light-response curves differed depending on cane type and time of year. A temporal convergence of sink demand from fruit, primocanes, and roots occurs when plants experience high temperatures. These factors may account for low red raspberry yield.

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Silvana Nicola, Luigi Basoccu, and Salvino Leoni

Excessive nitrogen can be detrimental to transplant quality when supplied during the period of suboptimal photoperiod conditions. This investigation was made to determine the relationship between nitrogen and photoperiod on the growth rate of the transplants. The growth analysis included the determination of the net assimilation rate (NAR) and the nitrogen productivity (NP). `Camone' tomato (Lycopersicon esculentum Mill.) seedlings were grown in the greenhouse under two photoperiods 8 and 12 h) at a constant light intensity and fertilized with three different N concentrations (8, 15, and 30 mmol·liter–1) applied four times. Longer photoperiods enhanced plant growth by increasing the internode, LAR, SLA, and SWR. Root fresh weight, dry weight, stem dry matter, NAR, and RWR were minimal when 30 mmol·liter–1 N concentration was supplied, while LAR and SLA were at their maximum level. The interaction between N and photoperiod was significant. Increasing N supply during an 8-h photoperiod decreased growth. During a 12-h photoperiod, 15 mmol·liter–1 was the optimum N concentration for fresh growth and 8 mmol·liter–1 for shoot dry growth. The RGR had the lowest value, with 30 mmol·liter–1 N and 8-h photoperiod. PNC was highest when plants received 30 mmol·liter–1 N during an 8-h photoperiod, and when the plants received 15 and 30 mmol·liter–1 N during the 8-h photoperiod. LNC doubled in plants fertilized with 30 mmol·liter–1 N compared to those with 8 mmol·liter–1 when grown under a 12-h photoperiod. The NP was at the maximum in plants fertilized with 8 mmol·liter–1 N at the 12-h photoperiod. The lowest NP values occurred when plants were fertilized with 30 mmol·liter–1 N. When photoperiod is a limiting factor in growing seedlings, N supply must be limited to optimize the efficiency of its utilization by the plant.

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B. Murillo-Amador, E. Troyo-Dieguez, and F. orrego-Escalante

The response of physiological traits of four genotypes of Opuntia spp (AN-V1, AN-V3, AN-V5, and AN-TV6) to organic fertilization with two levels of thickness and different plant densities (10, 20, 30, 40, and 50 plants/m2) under plastic tunnels were studied in the Universidad Autnoma Agraria “Antonio Narro” in 1995 and analyzed at CIBNOR, La Paz, Mexico. The main goal of this work was to screen Opuntia genotypes for yield and photosynthetical efficiency. The experiment was established as a randomized blocks design with three replicates. Response variables were dry weight (DW), crop growth ratio (CGR), rate of crop growth (RCG), relative growth rate (RGR), leaf area index (LAI), and net assimilation rate. The annual average temperature in the study site was 19.8°C. Hottest months were July and August, with temperature values as high as 39°C. The lowest temperatures were recorded in December and January, with temperatures as low as –13°C. Annual rainfall was 365 mm. Soils in the study region show a generalized low fertility. According to our results, genotype AN-V1 showed the best photosynthetical features with 30 plants/m2; genotype AN-TV6 showed no differences for 40 and 50 plants/m2. The highest values for CGR and RCG were observed under the highest level of organic fertilization (16-cm thickness). Genotypes AN-V3 and AN-V5 evidenced the highest RCG. Other results suggest that AN-V3 and AN-V5 showed the highest value for LAI, for a density 50 plants/m2, and genotypes AN-V1 and AN-V3, with a density 40 plants/m2, had the highest RGR. The studied Opuntia genotypes appeared to be promising crops for marginal semiarid regions.

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Keith A. Funnell, Errol W. Hewett, Ian J. Warrington, and Julie A. Plummer

Dry matter accumulation and partitioning in plants of Zantedeschia Spreng. `Best Gold' aff. Z. pentlandii (Wats.) Wittm. (syn. Richardia pentlandii Wats.) were quantified under a range of temperature and photosynthetic photon flux (PPF) regimes using plant growth analysis. The relative rate of dry matter accumulation [relative growth rate (RGRM), g·g-1·d-1] was highly correlated with the partitioning of the daily increment of dry matter into leaf tissue [leaf matter partitioning (LMP), g·d-1 per g·d-1]. In contrast, a poor correlation existed between RGRM and net assimilation rate (NAR, g·m-2·d-1). Maximum values of RGRM increased linearly with increasing temperature (from 13 to 28 °C), with a base temperature of 2.1 ± 2.7 °C. The optimum temperature for growth was PPF dependent with maximum total plant dry mass occurring under high PPF (694 μmol·m-2·s-1) at 25 °C. However, as the plant responded to PPF by altering LMP, final total plant dry mass was actually greater under the low PPF regime (348 μmol·m-2·s-1) at temperatures <22 °C. The optimum temperature for dry matter accumulation was close to the average daily air temperature during the growing season for the natural habitat of the parent species. Similarly, the greater dry matter accumulation under the combination of either low PPF and cooler temperatures or high PPF and warmer temperatures was paralleled by the diversity of PPF habitats in the natural open grassland and forest margin the parent species occupies. It is therefore suggested that Zantedeschia `Best Gold' is well adapted to optimize growth under these environmental conditions.

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Serge Yelle, Richard C. Beeson Jr., Marc J. Trudel, and André Gosselin

Lycopersicon esculentum Mill. cv. Vedettos and Lycopersicon chmielewskii Rick, LA 1028, were exposed to two CO2 concentrations (330 or 900 μmol·m-3) for 10 weeks. The elevated CO2 concentration increased the relative growth rate (RGR) of L. esculentum and L. chmielewskii by 18% and 30%, respectively, after 2 weeks of treatment. This increase was not maintained as the plant matured. Net assimilation rate (NAR) and specific leaf weight (SLW) were always higher in C02-enriched plants, suggesting that assimilates were preferentially accumulated in the leaves as reserves rather than contributing to leaf expansion. Carbon dioxide enrichment increased early and total yields of L. esculentum by 80% and 22%, respectively. Carbon exchange rates (CER) increased during the first few weeks, but thereafter decreased as tomato plants acclimated to high atmospheric CO2. The relatively constant concentration of internal C0 with time suggests that reduced stomatal conductance under high CO2 does not explain lower photosynthetic rates of tomato plants grown under high atmospheric CO2 concentrations. Leaves 5 and 9 responded equally to high CO2 enrichment throughout plant growth. Consequently, acclimation of CO2-enriched plants was not entirely due to the age of the tissue. After 10 weeks of treatment, leaf 5, which had been exposed to high CO2 for only 10 days, showed the greatest acclimation of the experiment. We conclude that the duration of exposure of the whole plant to elevated CO2 concentration, rather than the age of the tissue, governs the acclimation to high CO2 concentrations.