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P.R. Knight, J.R. Harris, J.K. Fanelli, and M.P. Kelting

Two experiments were conducted on Acer rubrum L. to determine the influence of root severance on sap flow, stomatal conductance, leaf water potential (ψ), and stem xylem embolism. Experiment 1 utilized 3-year-old trees, and experiment 2 utilized 2-year-old trees. Sixteenmm sap flow gauges were installed on both groups. Trees for experiment 1 were harvested on 31 May 1996 with a root ball diameter of 30.5 cm. Sap flow was reduced within one day after plants were harvested and was still lower 1 week after harvest. On 7 June 1996, harvested trees had lower stomatal conductance measurements, compared to not-harvested trees, but ψ were similar. A second experiment was initiated on 20 Aug. 1996, using the same protocol as in experiment 1. Sap flow was reduced within 2 h after harvest for harvested trees compared to not-harvested trees. Leaf stomatal conductances were reduced within 4 h of harvest. Leaf water potentials were not influenced on the day that the trees were harvested. Embolism levels were increased by harvest within 24 h. These results indicate that transplant stress begins shortly after harvest and not at the actual time of transplant.

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Kathryn Wimberley and Dr. Pat Williams

Kentucky West Nursery Cooperative, producers of pot-in-pot trees, needed recommendations on slow-release fertilizer applications due to regional environmental influences affecting production. Murray State University established a pot-in-pot tree nursery to research these influences in 2004. Two different fertilizer applications in three different treatments were tested on one-year old bare-root whips of Acer rubrum `Red Sunset' and `Autumn Blaze'. These trees were planted in 100% pine bark in 15-gallon pots and placed in the sockets with a complete random split-block design. Drip irrigation by spray stakes watered each pot. Nursery floor was kept clean by landscape fabric. New growth was pruned as needed to keep the trees within nursery standards. Tree calipers were measured on 1 Apr. and 1 Dec. 2004 at the beginning and end of growth. Leaves for chlorophyll readings were randomly selected to measure nitrogen uptake in late summer. Measurements were analyzed by SAS 9.1 and results found no significant differences among the treatments either in caliper increase or in chlorophyll levels (SAS, 2002). This experiment recommends a treatment using one application of slow-release fertilizer, versus split or additional applications, provides equal, quality growth of Acer rubrum `Autumn Blaze' and `Red Sunset'. The information gathered will direct fertilizer applications for KWNC and reduce their labor costs.

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Louis Anella and Thomas H. Whitlow

Changes in photosynthesis and root morphology during flooding were studied in container-grown 2- to 3-year-old Acer rubrum L. saplings. The seed was collected from opposite ends of a hydrologic gradient: two upland xeric sites [the George Washington National Forest in Page County, Va. (38°25'N, 78°35'W), and the Robinson Forest in Perry County, Ky. (37 °9'N, 83°7'W)] and a floodplain hydric site [the Presquile National Wildlife Refuge along the James River in Chesterfield County, Va. (37°21'N, 77°16'W)]. Each xeric site, containing various half-sib families (maternal parent known, paternal parent from one or more sources), was compared to a different hydric site half-sib family. After 1 week of flooding, the xeric-site trees had lower net photosynthesis than the hydric-site trees and remained significantly lower for the duration of the study. After an initial drop, hydric-site plants showed a recovery in net photosynthesis, indicating a greater ability to acclimate to a flooding stress. Seventy-one percent of the hydric-site plants developed adventitious roots and all retained their leaves. Xeric-site plants did-not develop adventitious roots and 61% were defoliated after 60 days of continuous flooding. The results indicate ecotypic differentiation in physiological response between Acer rubrum populations collected from opposite ends of a hydrologic gradient.

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Timothy J. Smalley and Carleton B. Wood

Commonly used planting techniques and soil amendments were compared to determine their effect on root growth, shoot growth, and drought tolerance of 2.5 cm caliper Acer rubrum. Study I: Trees were planted on 6 April 1992 into holes backfilled with 1) native soil, 2) 50% aged pine bark: 50% native soil, 3) 50% Mr. Natural™:50% native soil, or 4) 100% Mr. Natural™. Mr. Natural™ consists of granite sand, expanded shale, and composted poultry litter. After two years, no differences in growth or survival existed. Study II: On 8 April 1992, trees were planted in 1) unamended planting holes, 2) tilled planting beds, or 3) tilled and pine bark-amended planting beds. Five months after planting, the root growth in the tilled and tilled-amended beds did not differ, but both had more root growth than planting holes. Amendment-induced nitrogen deficiency reduced shoot growth of the tilled-amended treatment during the first year. After two years, the planting hole treatment exhibited the least shoot growth, while shoot growth of tilled and tilled-amended treatments did not differ. StudyIII: Selected trees in study II were drought stressed for 8 weeks beginning 4 August 1993. No differences in relative leaf water content among treatments were observed Results suggest that native soil should be used as backfill in planting holes; however, tilling a planting bed increases root and shoot growth compared to planting in a hole. Amending beds with pine bark did not increase growth or drought tolerance.

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Patricia R. Knight, J. Roger Harris, and Jody K. Fanelli

Root severance during field harvesting alters the water status of a tree, resulting in water stress and reduced post-transplant growth. Two experiments, using Acer rubrum L. (red maple), determined the influence of root severance at harvest on sap flow and xylem embolism. Trees 1.5–1.8 m tall (4 years old) were utilized in the first experiment, and trees 1.2–1.5 m tall (2 years old) were utilized in the second. Sap flow sensors were installed on the 4-year-old trees prior to root severance and remained on the trees until 1 week after harvest. Within 1 day after root severance sap flow was reduced and remained lower than nontransplanted (control) trees for the remainder of the experiment. Leaf stomatal conductance (Cs) of transplanted trees 1 week after root severance was lower than that of control trees, but leaf water potentials (ψ) were similar. In the second experiment, sap flow was reduced relative to control trees within 2 h after root severance. Although Cs was reduced 4 hours after root severance, ψ was not. Embolism increased within 24 hours of root severance. These results indicate that root severance quickly induces increased levels of embolism, which is associated with reduced sap flow.

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P. Eric Wiseman and Christina Wells

Arbuscular mycorrhizal fungi (AMF) form a symbiotic relationship with numerous landscape tree species and can improve tree growth and environmental stress tolerance. Construction-related soil disturbance is thought to diminish AMF colonization of transplanted trees in newly developed landscapes. We gathered root, soil, and foliar data from red maples (Acer rubrum) growing in newly developed landscape sites and adjacent native forest sites to test the hypotheses that: 1) landscape trees show lower levels of AMF colonization than forest trees; and 2) the AMF inoculum potential of landscape soils is lower than that of forest soils. Fine roots sampled from landscape maples had significantly lower AMF colonization than maples from adjacent forest sites (3% vs. 22%; P= 0.0002). However, soil-sand mixtures made from landscape soils possessed greater AMF inoculum potential than those made from forest soils (10% vs. 4%; P= 0.0081). Forest soils were more acidic and possessed less extractable P than landscape soils, and differences in AMF colonization between forest and landscape maples appeared to reflect differences in soil chemical properties rather than in soil inoculum potential.

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W.L. Bauerle, T.H. Whitlow, T.L. Setter, and F.M. Vermeylen

Quantitative differences in leaf abscisic acid (ABA) among Acer rubrum L. (red maple) ecotypes were investigated. This study tested the hypothesis that seedlings from wet and dry maternal sites display distinctly different capacities to synthesize ABA in response to atmospheric vapor pressure deficits. The increased levels of ABA in leaf tissue in the red maple ecotypes were associated with atmospheric vapor pressure deficit (VPD). Leaves on well-watered plants responded to VPD by increasing their ABA levels and reducing their photosynthesis (Anet) and stomatal conductance (gs). Both ecotypes appear to accumulate ABA at about the same rate as VPD increased. Despite the similar accumulation rates between ecotypes, wet site ecotypes consistently had a higher level of ABA present in leaf tissue under both low and high VPD conditions. Furthermore, wet site provenances appear to reduce Anet and gs in response to ABA accumulation, whereas dry sites do not present as clear an ABA/gs relationship. This study shows variation between wet and dry site red maple populations in physiological response to atmospheric vapor pressure deficits, indicating that natural ecotypic variation in stomatal responsiveness to air humidity is likely mediated by ABA accumulation in leaf tissue. This research demonstrates that ecotypes of red maple may be selected for atmospheric drought tolerance based on site moisture conditions.

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T.J. Smalley, M.A. Dirr, A.M. Armitage, B.W. Wood, R.O. Teskey, and R.F. Severson

Leaf water status, carbohydrate levels, net photosynthesis, stomatal conductance, ABA, dihydrozeatin riboside (DHZR), and trans-zeatin riboside (ZR) levels were determined in a greenhouse during rooting of stem cuttings of Acer rubrum L. `Red Sunset' taken on 3 Sept. 1987 and 28 May 1988. Leaf water status deteriorated before rooting and improved after root emergence. Leaf carbohydrate concentrations (glucose, sucrose, total soluble sugars, and total carbohydrates) increased until rooting and decreased after rooting, while changes in starch concentrations were trendless. ABA levels increased after insertion of cuttings into the rooting medium, but decreased before rooting. No correlation between timing of rooting and concentrations of the cytokinins ZR or DHZR was observed. Photosynthetic rates during rooting were higher for the Sept. 1987 cuttings and did not decrease to the compensation point as did those for May 1988 cuttings. Low photosynthetic rates and stomatal conductance of the cuttings during rooting were associated with water stress. The relationship between photosynthetic rates of such cuttings and cytokinin (CK) or ABA content was unclear. Chemical names used: [S-(Z,E]-5-(1-hydroxy-2,6,6-trimethyl-4-oxo-2-cyclohexen-1-yl)-3-methyl-2, 4-pentadienoic acid (abscisic acid, ABA); 2-methyl-4-(1H-purin-6-ylamino)-2-buten-1-ol (zeatin, Z).

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P.R. Knight, J.R. Harris, and J.K. Fanelli

Year-old seedlings of Acer rubrum L. and Crataegus phaenopyrum (L.f.) Medic. were grown for 1 year in a Groseclose silty clay loam. Seventy-two plant per species were harvested on 15 Dec. 1995 and weighed. Plants were stored at 4°C for 0, 1, 3, 5, 10, or 15 weeks. At the end of each storage period, 12 plants were weighed to determine water loss. Six plants were then sacrificed to determine percent embolism, and six plants were planted in a pine bark media and grown in a glasshouse for 15 weeks to determine the influence of storage on post-transplant growth and embolism recovery. Length of storage had no influence on embolism of Crataegus. Embolism of Acer increased linearly with increasing length of storage. Embolism was greater for Crataegus compared to Acer at each harvest. Water loss for both species increased linearly as time of storage increased.

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William L. Bauerle, William W. Inman, and Jerry B. Dudley

Quantitative differences in leaf abscisic acid (ABAL) among four cultivars of red (Acer rubrum L.) and one Freeman maple (Acer × freemanii E. Murray) were investigated. This study tested the hypothesis that ABAL concentration can be used to compare the effects of water stress on the gas exchange response of five different maple cultivars, including four red maple genotypes, `Summer Red', `October Glory', `Autumn Flame', and `Franksred' (Red Sunset), as well as one hybridized Freeman maple genotype, `Jeffersred' (Autumn Blaze). Cloned genotypes of red and Freeman maple were subjected to two treatments: 1) irrigated daily to container capacity or 2) irrigation withheld for one drought and recovery cycle. Leaf abscisic acid concentration, gas exchange, and whole-tree sap flow measurements were conducted under both conditions. Over the course of the drought stress and recovery phase, net photosynthesis (Anet), stomatal conductance (gs), and transpiration (E) declined as ABAL and instantaneous water use efficiency (A/gs) increased. This study found that ABAL tracked gs and that stomatal responsiveness to substrate moisture deficit is likely mediated by ABA accumulation in leaf tissue. This research demonstrates a leaf-level physiological response to substrate volumetric water content that appears to depend on ABAL concentration. In addition, the evidence in this study indicates that ABAL may be used as a potential surrogate for the gs response to substrate water stress and could become part of a cultivar drought tolerance selection strategy for red and Freeman maple.