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Single-node cuttings of `Autumn Flame' and `Indian Summer' red maple (Acer rubrum L. and A. × freemanii E. Murray) were placed in subirrigated perlite that was kept at 29, 33, or 36 C at the cut ends for 3 weeks. Number and mass of roots and pigment quality and transpiration of leaves were greater for `Autumn Flame' than `Indian Summer' and decreased with increasing temperature for both cultivars. Rooting percentage at 29, 33, and 36 C was 75, 75, and 25 for `Autumn Flame' and 13, 13, and 0 for `Indian Summer'. Earlier work has shown > 90% of cuttings of both cultivars root at ≈ 22 C, and plants of `Autumn Flame' are more heat resistant than those of `Indian Summer'. Results of this experiment suggest the effect of heat on rooting of cuttings might be used to predict genotypic differences in heat resistance of whole plants.

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Along with its horticultural uses, silver maple (Acer saccharinum L.) can be grown for biomass in areas that vary greatly in annual rainfall and temperature. Silver maples from five provenances ranging from 33 to 46° N latitude were subjected to drought stress and to high root-zone temperature (RZT) in separate experiments to assess their suitability as biomass sources. In the drought experiment, control plants were irrigated every 2 days, while stressed plants were irrigated every 15 days. Initial results indicated provenance differences among control plants in dry mass, leaf area, and transpiration. Drought reduced growth and mitigated differences among provenances. Osmotic potential of leaves was higher in control plants than in drought-stressed plants. Plants from two provenances (33 and 44° N) were grown with RZT of 24 and 34 C for 3 weeks. Gain in fresh mass over time was reduced at 34 C for plants of both origins, but plant dry matter and leaf surface area were similar at the two RZT. Data collected to date suggest resistance to drought and high RZT is similar in plants of different provenances.

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Maackia amurensis Rupr. & Maxim. is a leguminous tree with potential for increased use in urban landscapes. Information on the nutrition of M. amurensis is limited. To our knowledge, modulation and N2 fixation have not been reported. Our objective was to examine M. amurensis for nodulation and N2 fixation. Soil samples were collected near legume trees at arboreta throughout the United States, with additional samples from Canada and China. Seedlings were grown for six weeks in a low-N, sterile medium and inoculated with soil samples. Upon harvest, small white nodules were found on the lateral and upper portions of the root systems. Bacteria were isolated from the larger nodules, subculture, and used to inoculate seedlings. Inoculated plants nodulated and fixed N2 as determined by the acetylene reduction assay. We conclude M. amurensis forms N2-fixing symbioses with Rhizobium.

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High temperatures are reported to promote day-neutral strawberry (Fragaria ×ananassa) vegetative growth and development and inhibit floral and fruit development, thereby imposing geographic and temporal limitations on fruit production. Day-neutral strawberry response to air temperature has been researched, but specific responses to temperature in the root zone have not. In a 1998 greenhouse experiment, 60 `Tristar' plants were grown hydroponically in a system of individual, temperature-controlled pots. A randomized complete-block design with constant root-zone treatments of 11, 17, 23, 29, and 35 °C and 12 replications were used. Stomatal conductance and transpiration rate were significantly lower for plants at 35 °C, compared with plants at all other temperatures. Leaf area and leaf dry mass of plants at 35 °C were five and four times smaller, respectively, than the combined mean for plants in all other treatments. Leaf area of runner tips was 450 and 44.5 cm2 at 11 and 35 °C, respectively, compared with that of plants at all other temperatures, 1552.1 cm2. Fruit dry mass was 14.5, 21.6, 25.5, 29.0, and 3.96 g per plant at 11, 17, 23, 29, and 35 °C, respectively. Root dry mass was highest at 11 and 17 °C and lowest for plants at 35 °C. The number of flowers, fruit, and inflorescences per plant was reduced at 35 °C, as were individual berry fresh mass and diameter. Overall, `Tristar' growth and development were near optimal at 17, 23, and 29 °C.

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Temperature, as a potential environmental stressor, interacts with photoperiod in floral initiation of June-bearing strawberries (Fragaria ×ananassa), such that high-temperature exposure can result in poor floral initiation. Our objectives were to examine the effects of various durations of high root-zone temperature on floral initiation and development and on vegetative growth and development. In a 1998 greenhouse experiment, hydroponically grown `Allstar' June-bearing strawberry plants were subjected day/night temperatures of 31/21 °C in the root zone for one, two, or three continuous periods (of ≈7 days), followed by exposure to 17 °C for the duration of the experiment. Control plants were raised at 17 °C in the root zone throughout the experiment. An additional temperature treatment was exposure to 31/21 °C in the root zone for two periods, each followed by a period at 17 °C. Plants were arranged in a randomized complete-block design with factorial treatments of duration of high root-zone temperature and harvest time. At the end of each period, plants were harvested and the apical meristems dissected for microscopic evaluation of vegetative and floral meristems and the stage of development of the primary flower. We observed floral initiation in all treatments after photoperiodic induction. However, exposure to 31/21 °C in the root zone during key periods of floral initiation in June-bearing strawberry may alter floral development.

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Our objectives were to quantify the growth and quality of herbaceous annuals grown in different types of bioplastic-based biocontainers in commercial greenhouses and quantify producer interest in using these types of biocontainers in their production systems. Seedlings of ‘Serena White’ angelonia (Angelonia angustifolia) and ‘Maverick Red’ zonal geranium (Pelargonium ×hortorum) that had been transplanted into nine different (4.5-inch diameter) container types [eight bioplastic-based biocontainers and a petroleum-based plastic (PP) (control)] were grown at six commercial greenhouses in the upper midwestern United States. Plants were grown alongside other bedding annuals in each commercial greenhouse, and producers employed their standard crop culture practices. Data were collected to characterize growth when most plants were flowering. Questionnaires to quantify producer perceptions and interest in using bioplastic-based biocontainers, interest in different container attributes, and satisfaction were administered at select times during the experiment. Container type interacted with greenhouse to affect angelonia growth index (GI) and shoot dry weight (SDW), as well as shoot, root, and container ratings. Container type or greenhouse affected geranium GI and shoot rating, and their interaction affected SDW, and root and container ratings. These results indicate that commercial producers can grow herbaceous annuals in a range of bioplastic-based biocontainers with few or no changes to their crop culture practices.

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We quantified the growth and quality of ‘Arizona Sun’ blanket flower (Gaillardia ×grandiflora) grown in different bioplastic containers and characterized the interest of commercial perennial producers in using bioplastic-based biocontainers in their herbaceous perennial production schemes. Plants were grown in three types of #1 trade gallon (0.75 gal) containers at five commercial perennial producers in the upper-midwestern United States. Containers included one made of polylactic acid (PLA) and a proprietary bio-based filler derived from a coproduct of corn ethanol production, a commercially available recycled paper fiber container twice dip-coated with castor oil–based biopolyurethane and a petroleum-based plastic (control) container. Plant growth data were collected when most plants had open flowers, and plant shoots, roots, and containers were rated by commercial grower participants. Questionnaires were administered at the beginning and at the end of the experiment to characterize the perceptions and interest of growers in using these containers, their interest in different bioplastic-based container attributes, and their satisfaction from using the containers. Container type and grower interacted to affect growth index (GI), shoot dry weight (SDW), and container rating. Root rating was affected by container type or grower and shoot rating was unaffected by either. Our results indicate that commercial producers can adapt these bioplastic-based biocontainers to blanket flower production with few or no changes to their crop cultural practices.

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As part of a project to develop and assess bio-based, biodegradable plastics for their potential to replace petroleum-based plastics in specialty-crop containers, we evaluated prototype containers made of protein-based polymers from soybean [Glycine max (L.) Merr.] for their effectiveness during production of plants in greenhouses and subsequent establishment of those plants outdoors. Our objective was to assess the function and biodegradation of soy-based plastic containers with special attention to whether a fertilizer effect results from degrading containers before and after plants are moved outdoors. In our first experiment, plants of tomato (Solanum lycopersicum L.) and pepper (Capsicum annuum L.) were grown in soy-plastic containers and control containers of petroleum-based (polypropylene) plastic under greenhouse conditions for 4 weeks. Each plant then was transplanted and grown in an outdoor garden plot for 5 weeks with the container removed, broken into pieces less than 4 cm in diameter, and installed beneath the roots of the transplant. Three additional experiments were performed: a greenhouse trial to quantify the relative concentration and form of plant-available nitrogen (N) released from soy-plastic containers of three types [soy plastic, soy plastic coated with polylactic acid (PLA), and soy–PLA polymer blended 50:50 by weight] during production; a greenhouse trial to evaluate the same three container types under production conditions with five container-crop species; and a field trial to assess the effects of the 50:50 soy–PLA container on transplant establishment. Plant-available N was released from soy-based plastic containers during greenhouse production, and transplant establishment was enhanced when the soy-based container was removed, crushed, and installed in the soil near plant roots. During greenhouse production, containers of high-percentage soy plastic released N at an excessive rate (623 mg·L−1 in leachate) and predominantly in the form of NH4 + (99.4% at 3 weeks of culture). Containers made by blending soy plastic with PLA released N at a favorable rate during production. In both field trials, growth and health of plants cultured in soy containers were better than those of controls. Although the design and material formulation of soy-plastic containers need to be improved to optimize container integrity and plant health during production, our results illustrate the potential to use soy-based plastics in biodegradable containers that release N at rates that promote growth and health of plants during greenhouse production and establishment of transplants outdoors.

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Freeman maples (Acer ×freemanii E. Murray) are suspected to be more resistant to environmental stress than red maples (A. rubrum L.) because the lineage of Freeman maple includes silver maple (A. saccharinum L.). Little is known, however, about stress resistance of silver maple, and few data from direct comparisons of red and Freeman maples are available. Our objectives were to determine effects of root-zone heat on silver maples from northern and southern provenances, and to compare red and Freeman maple cultivars for resistance to rootzone heat stress and drought. There were no provenance-by-temperature interactions when silver maples from 33.3°N (Mississippi) and 44.4°N (Minnesota) latitude were grown with root zones at 29 and 35°C. Plants from 44.4°N latitude had 36% higher fresh mass, 43% more leaf surface area, and 35% and 59% higher, respectively, root and shoot dry masses than plants from 33.3°N latitude. Midday xylem water potential was 68% more negative for plants at 35°C than for plants at 29°C, and transpiration rate was 129% less for plants with root zones at 35°C than for those with root zones at 29°C. During preliminary work with Autumn Flame and Franksred red maple and Indian Summer and Jeffersred Freeman maples, rooted cuttings were grown in 25 and 37°C root zones under both drought and nondrought conditions. Reductions in growth at 37°C were similar for all cultivars. Results of this work could influence development, marketing, and use of Freeman maples.

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Bioplastics and bioplastic composites are a group of emerging sustainable materials that exhibit favorable characteristics for use in horticulture-production containers. Biocontainers made from composite materials of soy [Glycine max (L.) Merr.] bioplastic and poly(lactic) acid (PLA) have been shown to release nitrogen (N) at a rate suitable for supporting plant growth. We hypothesized that fertilizer applications can be reduced while maintaining adequate nutrition levels for plant production when using soy-based containers. To test this hypothesis and quantify potential reduction of fertilizer, we grew marigold ‘Honeycomb’ (Tagetes patula L.) in five prototypes of soy-composite biocontainers [soy bioplastic compounded with PLA or polyhydroxyalkanoates (PHA)] and a petroleum-plastic (polypropylene) control container with five fertilizer treatments supplying 1) 60N‒4P‒49K; 2) 75N‒5P‒61K; 3) 105N‒7P‒85K; 4) 150N‒10P‒122K; or 5) 300N‒20P‒244K mg. At harvest, plants grown in all soy‒PLA composite biocontainers and protein + PLA biocontainers had higher concentrations and contents of N and P compared with plants grown in petroleum-plastic containers across all fertilizer treatments. Shoot K concentrations were highest for plants grown in all soy‒PLA and soy‒PHA biocontainers compared with plants grown in petroleum-plastic containers across all fertilizer treatments, whereas shoot K concentrations in plants grown in protein + PLA biocontainers were equal to or lower than plants in petroleum-plastic containers. Total plant dry weight was greater for plants grown in biocontainers made of 50% soy‒50% PLA and protein + PLA than for plants grown in control containers across all fertilizer treatments except at the highest rate of fertilizer in which plants received 300N‒20P‒244K mg. Our results support the hypothesis that fertilizer inputs can be reduced when using soy-composite biocontainers. Biocontainers made with equal parts soy bioplastic and PLA showed strong potential for achieving adequate plant growth with reduced fertilizer input. Our results demonstrate that fertilizer can be reduced by as much as 80% when growing marigold in containers made of 50% soy‒50% PLA for 6 weeks.

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