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John M. Ruter and Dewayne L. Ingram

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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John M. Ruter and Dewayne L. Ingram

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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Charles R. Hall and Dewayne L. Ingram

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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Dewayne L. Ingram and Charles R. Hall

The objective of this study was to examine the differences in global warming potential (GWP) and variable cost structure of a 5-cm-caliper red maple tree grown using two alternative production methods including a traditional field [balled and burlapped (BNB)] production system and a containerized, pot-in-pot (PIP) production system. Feedback from nursery growers was obtained to model each production system including the labor required for each cultural practice, materials used, and the hourly usage of tractors and other equipment. Findings from the study indicate that the total system GWP and variable cost for the PIP tree system is −671.42 kg of carbon dioxide equivalent (CO2e) and $250.76, respectively, meaning that the tree sequesters much more carbon during its life than is emitted during its entire life cycle. The same holds true for the BNB tree; however, in this system, the GWP of the tree −666.15 kg CO2e during its life cycle at a total variable cost of $236.13. Thus, the BNB tree costs slightly less to produce than its PIP counterpart but the life cycle GWP is slightly less positive as well.

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Chris A. Martin and Dewayne L. Ingram

Leaf photosynthesis of Magnolia grandiflora `St. Mary' (13-month-old rooted cuttings) was studied when tree roots were exposed to 28, 35, or 42 ± 0.8C for 8 weeks. Root-zone temperature (RZT) treatments were sustained for 6 hours per day by an electronically controlled root-heating system. The experiment was conducted in a 3×7.5-m walk-in growth room. Growth room irradiance was supplied by eighteen 1000-W, phosphor-coated metal-arc HID lamps (photosynthetic photon flux = 600 μpmol-2·-1 at canopy height) for 13 hours daily augmented with 3 hours of incandescent light during the dark period. Leaf C assimilation (A) at an RZT of 42C decreased linearly over 8 weeks compared to leaf A at RZTs of 35 and 28C. Leaf A was similar for all trees at week 1; however, leaf A at an RZT of 42C was 30% and 34% less than at RZTs of 3.5 and 28C, respectively, at week 8. Stomatal conductance at RZTs of 28 and 35C increased linearly over 8 weeks compared to conductance at a RZT of 42C. Intercellular CO2 levels were not affected by RZT treatments. This finding suggests that reductions in leaf A were nonstomatal. Photosynthetic inhibition resulted in reduced shoot and root growth. Operators of outdoor container production nurseries should implement cultural practices that minimize exposure of tree roots to RZTs >35C.

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Chris A. Martin and Dewayne L. Ingram

Computer modeling was used to study the effect of container volume and shape on summer temperature patterns for black polyethylene nursery containers filled with a 4 pine bark: 1 sand (v/v) rooting medium and located in Phoenix, Ariz. (lat. 33.5°N, long. 112°W) or Lexington, Ky. (lat. 38.0°N, long. 84.4°W). For both locations, medium temperatures were highest at the east and west container walls, halfway down the container profile, regardless of container height (20 to 50 cm) or volume (10 to 70 liters). The daily maximum medium temperature (Tmax) at the center was lower and occurred later in the day as container volume was increased because of an increased distance to the container wall. For both locations, predicted temperature patterns in rooting medium adjacent to the container wall decreased as the wall tilt angle (TA) increased. Predicted temperature patterns at the center of the container profile were lowered in response to the interaction of increased container height and wall TA. As container height decreased, the container wall TA necessary to lower center Tmax to ≤ 40C increased; however, the required increase in TA was greater for Phoenix than for Lexington, principally because of higher ambient air temperatures.

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Carey Grable, Joshua Knight, and Dewayne L. Ingram

Although controlled-release fertilizers (CRFs) have been used in container-grown ornamental plants for decades, new coating technologies and blends of fertilizers coated for specific release rates are being employed to customize fertility for specific environments and crops. A study was conducted in the transitional climate of Kentucky to determine the nutrient release rates of three controlled-release blends of 8- to 9-month release and growth response of ‘Double Play Pink’ japanese spirea (Spiraea japonica) and ‘Smaragd’ arbovitae (Thuja occidentalis). Fertilizer 1 (16N–3.5P–8.3K–1.8Mg + trace elements) and Fertilizer 2 (18N–3.1P–8.3K–1.8Mg + trace elements) were prototype blends with different experimental polymer coatings. Fertilizer 3 was a blend of 18N–2.2P–6.6K–1.1Ca–1.4Mg–5.8S + trace elements, which combined 100% resin-coated prills with a polymer coating. Fertilizer 4 was commercially available 15N–3.9P–10K–1.3Mg–6S + trace elements. Fertilizer 3 released its nutrients earlier in the 12-week study than the other three fertilizers and resulted in lower shoot dry weight in both species. The new polymer coating technologies show promise for delivering a predicted release rate and are appropriate for container production of these woody shrubs in Kentucky. An interesting side note of this experiment was that leachate pH measurements across treatments averaged 1.2 units lower for arbovitae (6.3) than for japanese spirea (7.5) at week 12. It was assumed that chemical and/or biological reactions at the root/substrate interface in arbovitae moderated pH increases over the study.

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Dewayne L. Ingram and Charles R. Hall

Previously published life cycle assessment (LCA) studies regarding the global warming potential (GWP) of tree production have shown that the carbon footprint during the cradle-to-grave life cycle of a tree can reduce atmospheric CO2. This study provides another unique contribution to the literature by considering other potential midpoint environmental impacts such as ozone depletion, smog, acidification, eutrophication, carcinogenic or non-carcinogenic human toxicity, respiratory effects, ecotoxicity, and fossil fuel depletion for 5-cm-caliper, field-grown, spade-dug trees. Findings from this study validate using data from various literature sources with a single-impact focus on GWP and compiled and calculated in a spreadsheet or using a LCA software package with embedded databases (SimaPro) to generate comparable GWP estimates. Therefore, it is appropriate to use SimaPro to generate midpoint environmental impact estimates in LCA studies of field-grown trees. The authors also compared the midpoint environmental impacts with other agricultural commodities [corn (Zea mays), soybean (Glycine max), potato (Solanum tuberosum), and wool] and determined that trees compare favorably, with the exception that fossil fuel depletion for the trees was greater than the other products as a result of the high equipment use in harvesting and handling trees. In addition, the water footprint (WF) associated with tree production is also determined through LCA using the Hoekstra water scarcity method in SimaPro. The propagation-to-gate WF for the three tree production systems ranged from 0.09 to 0.64 m3 per tree and was highly influenced by irrigation water, which was the major contributor to WF for each production system. As expected, the propagation stage of each tree represented significantly less WF than the field production phase with larger plants and lower planting densities, even with more frequent irrigation/misting in liner production.

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John M. Ruter and Dewayne L. Ingram

Ilex crenata Thunb. `Rotundifolia' split-root plants were grown for 3 weeks with root zones at 30/30, 30/34, 30/38, 30/42, 34/34, 38/38, and 42/42C. The 38C root-zone treatment was the upper threshold for several growth and physiological characteristics. A portion of the root system grown at or near the optimum temperature could compensate, in terms of shoot growth, for part of the root system exposed to supraoptimal root-zone temperatures up to 38C. Higher root-zone temperatures did not affect short-term photosynthetic rates or root : shoot ratios, but altered photosynthate partitioning to various stem and root sinks. Although no differences were found for total 14C partitioned to the roots, partitioning of 14C into soluble and insoluble fractions and the magnitude of root respiration and exudation were influenced by treatment. Heating half of a root system at 38C increased the amount of 14C respired from the heated side and increased the total CO2respired from the nonheated (30C) half. Exposure of both root halves to 42C resulted in membrane damage that increased the loss of 14C-labeled photosynthates through leakage into the medium.

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John M. Ruter and Dewayne L. Ingram

Plants of `Rotundifolia' holly (Ilex crenata Thunb.) were grown for 3 weeks with root zones at 30,34,38, or 42C for 6 hours daily to evaluate the effects of supraoptimal root-zone temperatures on various photosynthetic processes. After 3 weeks, photosynthesis of plants grown with root zones at 38 or 42C was below that of plants grown at 30 or 34C. Chlorophyll and carotenoid levels decreased while leaf soluble protein levels increased as root-zone temperature increased. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) activity per unit protein and per unit chlorophyll responded quadratically, while RuBisCO activity per unit fresh weight increased linearly in response to increasing root-zone temperature. Results of this study suggest that `Rotundifolia' holly was capable of altering metabolism or redistributing available assimilates to maintain CO2 assimilation rates in response to increasing root-zone temperatures.