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- Author or Editor: Dewayne Ingram x
A three-dimensional computer model was developed to simulate numerically the thermal environment of a polyethylene container-root medium system. An energy balance was calculated at the exterior container wall and the root medium top surface. Thermal energy exchanges at the system's boundaries were a function of radiation, convection, evaporation, and conduction energy flaxes. A forward finite difference form of a transient heat. conduction equation was used to calculate rates of temperature changes as a result of thermal energy exchanges at the system's boundaries. The χ2“goodness-to-fit” test was used to validate computer-generated values to actual measured temperature data. Probabilities for the null hypothesis of no association ranged from P = 0.45 (Julian day 271), to P = 0.81 (Julian day 190), with P ≥ 0.70 on nine of 10 validation days in 1989. Relative to net radiation and convection, conduction and evaporation had little effect on thermal energy exchanges at the root medium top surface during sunlight hours. The rate of movement of thermal energy (thermal diffusivity) was slower and generally resulted in lower temperatures in a pine bark medium than in a pine bark medium supplemented with sand when volumetric water content (VMC) ranged from 0.25 to 0.45.
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.
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.
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.
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.
Abstract
Electrolyte leakage was used to measure direct heat injury to roots of Illicium anisatum L., Ilex cornuta L. cv. Burfordii and Juniperus chinensis L. cv. Parsonii. A sigmoidal relationship was found between percent electrolyte leakage and temperature treatment. About 50% electrolyte leakage was realized from a 20 minute exposure of roots to 50.5 ± 0.5°, 48.5 ± 0.5° and 46.5 ± 0.5°C for I. anisatum, J. chinensis, and I. cornuta, respectively.
Abstract
‘Mrs. G.G. Gerbing’ azaleas (Rhododendron L.), grown 12 months in a 2 pine bark : 1 Canadian peat : 1 sand (by volume) medium in 3-liter containers and fertilized with Woodace 14N-1P-2K compressed fertilizer tablets, had greater shoot and root dry weights if the medium was not amended with dolomitic limestone, compared to plants grown in the medium amended with dolomitic limestone at 3 kg/m3. Shoot and root dry weights were not different for plants grown with or without a superphosphate (9% P) amendment at 3 kg/m3 in combination with or without the dolomitic limestone amendment. Growing-medium Mn levels were greater (0.5 ppm) without the dolomitic limestone amendment, than with the amendment (0.06 ppm), whereas P levels were similar with or without the dolomitic limestone amendment. On day 60, growing-medium P levels were greatest (10 ppm) for the superphosphate-amended medium without dolomitic limestone and decreased to 0.5 ppm on day 300. Tissue P levels were not different with or without the superphosphate amendment in combination with or without dolomitic limestone.
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.
Seeds of Sophora secundiflora (Ort.) Lag ex. DC. (mescal bean) were scarified with hot water or concentrated sulfuric acid to determine an optimal pretreatment for successful germination. Scanning electron micrographs indicated that the acid scarification treatment removed the seed cuticle. One-year-old seeds were successfully stored and germinated ≈2 days sooner than from the current year if both were given an acid pretreatment. Germination rate increased as acid pretreatment time increased from 30 to 120 minutes. Soaking seeds in water at room temperature or in hot water (initially 93C) for 24 hours had no effect on germination.
Root growth of southern magnolia (Magnolia grandiflora Hort. `St. Mary') was studied for 16 weeks after an 8-week exposure to 30, 34, 38, or 42 ± 0.8C root-zone temperature (RZT) treatments applied for 6 hours daily. Immediately after RZT treatments, total root length of trees responded negatively to increased RZT in a quadratic pattern and the shoot and root dry weight of trees was similar. However, 8 and 16 weeks after RZT treatments, total root length responded linearly in a negative pattern to increased RZT, and shoot and root dry weight responded negatively to increased RZT in a linear and quadratic pattern, respectively. Root dry weight of trees exposed to 42C RZT treatment was 29% and 48% less than 38 and 34C RZT treatments, respectively, at week 8. By week 16, root dry weight as a function of RZT had changed such that the 42C RZT was 43% and 47% less than 38 and 34C RZT, respectively. Differences in root growth patterns between weeks 8 and 16 suggest that trees were able to overcome the detrimental effects of the 38C treatment, whereas growth suppression by the 42C treatment was still evident after 16 weeks.