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  • Author or Editor: Dewayne Ingram x
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Root growth of Magnolia grandiflora Hort. `St. Mary' was studied for 16 wk after an 8-wk exposure period to 30°, 34°, 38°, or 42°±0.8°C root-zone temperature (RZT) treatments applied 6 hr daily, Immediately after the RZT treatment period, total root length was similar for trees exposed to 30°, 34°, and 38°C and was reduced 45% at 42° compared to 38°C. For weeks eight and 18 of the post-treatment period, response of total root length to RZT was linear. Total root length of trees exposed to 28°C was 247% and 225% greater than those exposed to 42°C RZT at week eight and 16, respectively. Root dry weight from the 42°C RZT treatment was 29% and 48% less than 38° and 34°C RZT treatment, respectively, at week eight. By week 16, root dry weight as a function of RZT had changed such that the 42°C RZT was 43% and 47% less than 38° and 34°C RZT, respectively. Differences in root growth patterns between weeks eight and 16 suggest that trees were able to overcome the detrimental effects of the 38°C treatment whereas growth suppression by the 42°C treatment was still evident after 16 wk. Previous exposure of tree roots to supraoptimal RZT regimens may have long-term implications for suppressing growth and lengthening the establishment period of trees in the landscape,

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Root growth of Magnolia grandiflora Hort. `St. Mary' was studied for 16 wk after an 8-wk exposure period to 30°, 34°, 38°, or 42°±0.8°C root-zone temperature (RZT) treatments applied 6 hr daily, Immediately after the RZT treatment period, total root length was similar for trees exposed to 30°, 34°, and 38°C and was reduced 45% at 42° compared to 38°C. For weeks eight and 18 of the post-treatment period, response of total root length to RZT was linear. Total root length of trees exposed to 28°C was 247% and 225% greater than those exposed to 42°C RZT at week eight and 16, respectively. Root dry weight from the 42°C RZT treatment was 29% and 48% less than 38° and 34°C RZT treatment, respectively, at week eight. By week 16, root dry weight as a function of RZT had changed such that the 42°C RZT was 43% and 47% less than 38° and 34°C RZT, respectively. Differences in root growth patterns between weeks eight and 16 suggest that trees were able to overcome the detrimental effects of the 38°C treatment whereas growth suppression by the 42°C treatment was still evident after 16 wk. Previous exposure of tree roots to supraoptimal RZT regimens may have long-term implications for suppressing growth and lengthening the establishment period of trees in the landscape,

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Thermal properties of pine bark: sand container media as a function of volumetric water content and effectiveness of irrigation as a tool for modulating high temperatures in container media were studied. Volumetric water and sand content interacted to affect container medium thermal diffusivity. Adding sand to a pine bark container medium decreased thermal diffusivity if volumetric water content was less than 10 percent and increased thermal diffusivity if volumetric water content was between 10 and 70 percent. Thermal diffusivity was greatest for a 3 pine bark : 2 sand container medium if volumetric water content was between 30 and 70 percent. Irrigation was used to decrease temperatures in 10-liter container media. Irrigation water at 26°C was more effective if 1) volumes equaled or exceeded 3000 ml, 2) applications were made during mid-day, and 3) sand was present in the container medium compared to pine bark alone. However, due to the volume of water required to lower container media temperatures, nursery operators should first consider reducing incoming irradiance via overhead shade or container spacing.

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Respiration of excised Ilex crenata `Rotundifolia' roots as influenced by root-zone growth temperature and buffer solution temperature was measured in the presence and absence of SHAM and KCN. Respiration rates of roots excised from plants grown for three weeks at root-zone temperatures of 30, 34, 38, and 42 C decreased linearly as root-zone temperature increased when the buffer solution was maintained at 25 C. When the buffer solution temperature was the same as the root growth temperature, no differences in respiration rate were found. When plants were grown at a root-zone temperature of 30 C, respiration was maximal at 34 C and decreased to a minimum at 46 C. Above 46 C, stimulation of O2 consumption occurred which was presumed to be extra-mitochondrial. CN-resistant pathway activity decreased at a buffer solution temperature of 46 C which was similar to the critical threshold temperature (48±1.5 C) for `Rotundifolia' holly roots.

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High root-zone temperatures have been shown to affect photosynthate partitioning, respiration, nitrogen nutrition and growth of `Rotundifolia' holly. The loss of chlorophyll and protein in shoots of other plants in response to high root-zone temperatures has been documented. Therefore, the objectives of this research were to look at the effects of supraoptimal root-zone temperatures on RUBISCO activity, leaf protein and photosynthetic pigment levels.

Soluble protein levels in leaves increased linearly as root-zone temperature increased from 30 to 42 C. RUBISCO activity per unit protein and per unit chlorophyll responded quadratically to root-zone temperatures. Total chlorophyll, chlorophyll a & b, and carotenoid levels decreased linearly with increasing root-zone temperature. It is possible that `Rotundifolia' holly was capable of redistributing nitrogen to maintain RUBISCO activity for photosynthesis.

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Respiration of excised Ilex crenata (Thunb.) `Rotundifolia' roots as influenced by root-zone growth temperature and buffer solution temperature was measured in the presence and absence of salicylhydroxamic acid (SHAM) and potassium cyanide (KCN). Respiration rates of roots excised from plants grown for 3 weeks with root-zones at 30, 34, 38, or 42C decreased linearly with increased root-zone growth temperatures when the buffer solution was maintained at 25C. When the buffer solution was the same temperature as the root growth temperature, respiration rates were similar. Respiration in roots from plants grown with the root zone at 30C was maximal with the buffer solution at 34C and decreased to a minimum at 46C. Above 46C, a presumably extra-mitochondrial stimulation of O2 consumption occurred. The activity of the CN-resistant pathway was fully engaged (P' = 0.99) when roots were grown at 30C and buffer solution was at 25C (30-25). CN-resistant pathway activity decreased with `the buffer solution at 46C.

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University researchers have recently quantified the value of carbon sequestration provided by landscape trees (Ingram, 2012, 2013). However, no study to date has captured the economic costs of component horticultural systems while conducting a life cycle assessment of any green industry product. This study attempts to fill that void. The nursery production system modeled in this study was a field-grown, 5-cm (2-in) caliper Cercis canadensis ‘Forest Pansy’ in the Lower Midwest. Partial budgeting modeling procedures were also used to measure the sensitivity of related costs and potential benefits associated with short-run changes in cultural practices in the production systems analyzed (e.g., transport distance, post-harvest activities, fertilization rates, and plant mortality). Total variable costs for the seedling and liner stages combined amounted to $2.93 per liner, including $1.92 per liner for labor, $0.73 for materials, and $0.27 per liner for equipment use. The global warming potential (GWP) associated with the seedling and liner stages combined included 0.3123 kg of carbon dioxide equivalents (CO2e) for materials and 0.2228 kg CO2e for equipment use. Total farm-gate variable costs (the seedling, liner, and field production phases combined) amounted to $37.74 per marketable tree, comprised of $9.90 for labor, $21.11 for materials, and $6.73 for equipment use, respectively. However, post-harvest costs (e.g., transportation, transplanting, take-down, and disposal costs) added another $33.78 in labor costs and $27.08 in equipment costs to the farm-gate cost, yielding a total cost from seedling to end of tree life of $98.60. Of this, $43.68 was spent on labor, $21.11 spent on materials, and $33.81 spent on equipment use during the life cycle of each marketable tree. As per an earlier study, the life cycle GWP of the described redbud tree, including greenhouse gas emissions during production, transport, transplanting, take-down, and disposal, would be a negative 63 kg CO2e (Ingram et al., 2013). These combined data can be used to communicate to the consuming public the true (positive) value of trees in the landscape.

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This research uses a life cycle analysis and economic engineering approach to determine the costs and global warming potential (GWP) of production and post-production practices associated with Taxus ×media ‘Densiformis’, which is often grown using a more capital-intensive regime during the propagative and harvesting stages than the typical field-grown shrub. Total variable costs incurred during the rooted cutting stage were slightly over $0.24 per marketable rooted cutting. This was made up of $0.1966, $0.032, and $0.0127 for labor, materials, and equipment operating costs, respectively. The GWP of materials and equipment used during the rooted cutting stage of production was 0.0097 and 0.2762 kg CO2 equivalent (CO2e), respectively. Equipment costs in this phase were predominantly from heating the greenhouse (92%) and the greenhouse heating functions comprised 95% of the rooting cutting GWP. GWP during the post-farm gate stage was 2.4506 kg CO2e per marketable shrub but was offset by 12.5522 kg CO2 being sequestered in the shrub during its time in the landscape and weighted over the 100-year assessment period, leaving a net GWP of –8.1824 kg CO2e per marketable shrub by the end of the life cycle. Total takedown and disposal costs (labor) after an assumed 50-year life in the landscape were $9.0610. During the entire life cycle from cutting to landscape to takedown and disposal, total variable costs incurred were $17.9856 per shrub. These findings are consistent with previous studies in that the GWP is positive when considering the entire life cycle of the shrub from propagation to eventual removal from the landscape. Knowing the carbon footprint of production and distribution components of field-grown shrubs will help nursery managers understand the environmental costs associated with their respective systems and evaluate potential system modifications to reduce greenhouse gas (GHG) emissions.

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System-level research has resulted in significant advancements in horticultural crop production. Contributions of individual components to production efficiency, cost, and environmental impact have been a focus of such research. Public awareness of the environmental impact of products and services is increasing. Life cycle assessment (LCA) is a tool to study horticultural crop production systems and horticultural services and their individual components on environmental impacts such as the carbon footprint, stated as global warming potential. This manuscript introduces LCA and describes how this tool can be used to generate information important to the industry and consuming public.

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The demand for groundcover plants for landscape use is increasing. Plantable containers are becoming available in sizes appropriate for groundcover plants. Landscapers are seeking ways to decrease the time required to prepare and plant groundcover beds. Studies were conducted in 2011 and 2012 to evaluate plantable containers for a variety of groundcover plants. The study has shown that ‘Bronze Beauty’ ajuga (Ajuga reptans), ‘Herman’s Pride’ lamiastrum (Lamiastrum galeobdolon), ‘Beacon Silver’ lamium (Lamium maculatum), ‘Immergrunchen sedum (Sedum hybridum), ‘Red Carpet Stonecrop’ sedum (Sedum spurium), and ‘Vera Jameson’ sedum (Sedum telephium) were grown to a marketable size from 1.5-inch plugs in 8 weeks in Lexington, KY, when transplanted in May through August. ‘Big Blue’ liriope (Liriope muscari) from bare root bibs required 12 weeks. Plant growth in a 90-mm paper container and 80-mm bioplastic container was similar to that of plants grown in standard 3-inch rigid plastic containers and required 20% less time to transplant into the landscape and grew rapidly after transplanting in the field. Peat containers in this production system yielded smaller plants and slower ground coverage after transplanting in the field than plants grown in the other containers.

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