206 tional T. d. var. distichum from the central Texas (TX), and T. d. var. mexicanum (Montezuma cypress) from Mexico and southern Texas (MX) were evaluated for field growth, and tolerances to soil alkalinity, drought, and foliar and soil salinity (Denny 2007; Denny et al. 2008). From these multi-location regional seedling evaluations, 24 candidate clones were subsequently evaluated for vegetative rooting potential (King 2010; King et al. 2011; King et al. 2012) and clones with adequate rooting from the initial selec- tions were distributed to 10 sites. This encompassed sites in USDA plant hardiness zones 4b/5a to 10 (U.S. Dept. of Agriculture 1990). Test sites included an east-west transect in USDA plant hardiness zones 8 to 10 along the U.S. Gulf Coast stretching from central Florida (Balm, FL), the Florida Panhandle (Quin- cy, FL), central Texas (College Station, TX), to western Texas (El Paso, TX). A north-south transect from the Gulf Coast sites through the central U.S. was located in USDA plant hardiness zones 4b/5a, including northeastern Texas (Dallas, TX), the Texas panhandle (northern Texas) (Lubbock, TX), Arkansas (Fayetteville, AR), Kansas (Haysville, KS), Ohio (Columbus, OH), and Iowa (Ames, IA). Each test site used a single ramet of a given clone in each of three replications. Growth (height of main trunk, trunk diameter at 15 cm above the soil line), foliar chlorosis (percentage of the canopy exhibiting chlorotic or necrotic foliage), and field level cold tolerance (winter sur- vival, a qualitative rating of winter damage, and length of die- back of terminal branches) were evaluated (second-year data is presented herein, third-year is currently underway). Data from two representative clones from each of the three taxonomic groups (TD, TX, and MX) were chosen to illustrate the range of responses across environments and are presented herein. Quercus virginiana and Quercus fusiformis Complex Studies Acorns from four selected provenances were collected from the western range of Quercus virginiana Mill. and Quercus fusi- formis Small including the Southern Texas Plains (STP), Post Oak Savannah (POS), Lake Allen Henry Dam area in the Roll- ing High Plains (LAH), and the Brazos River Basin (Brazos). The accession from the STP is considered to be Q. virginiana. The POS accession is considered to be part of the hybrid swarm (and thus a potential hybrid) of Q. virginiana and Q. fusifor- mis. Simpson (1988) reports trees with intermediate character- istics likely representing a hybrid swarm between Q. virginiana and Q. fusiformis where their ranges overlap. The LAH acces- sion appears morphologically to be a hybrid of Q. fusiformis and the Brazos accession (Purnell 2010). Finally, the Brazos accession appeared morphologically to be a relictual popula- tion with characteristics not in keeping with any of the other accessions (Purnell 2010). These accessions were compared in various studies for taxonomy, drought tolerance, and land- scape growth characteristics (Purnell 2010). Results of an acute drought experiment are presented here, in which 100 seedlings from acorns of each of the provenances were germinated in moist sand and then transplanted into 15 cm diameter circu- lar pots containing a peatlite substrate (Metro-mix 200™ , Sun Gro Horticulture Canada, Ltd., Vancouver, British Columbia, Canada) and amended with 4 g of 31-0-0 Osmocote controlled release fertilizer (Scotts; Marysville, Ohio, U.S.). Plants were then placed on a greenhouse bench and were grown under stan- ©2012 International Society of Arboriculture Arnold et al.: Potential for Selecting More Sustainable Urban Trees dard greenhouse conditions. After establishment, the containers were placed in a randomized complete block design with a split plot arrangement with each experimental block containing one plant of each accession. The main plot was the Quercus series Virentes accession, and the split plot was the irrigation treat- ment. Half of the seedlings were subjected to intense drought stress by withholding all irrigation during the experiment. The remaining seedlings served as the control and were irrigated by hand to maintain plant-available soil moisture. Midday stomatal conductance readings (gs ) were taken weekly using from the same accessions were used to repeat the experiment. over the course of the season were assumed to be under greater stress than a tree with higher gs. A second set of plants a SC-1 porometer (Decagon Devices, Inc., Pullman, Washing- ton, U.S.). Measurements began at approximately 1200 HR on well-exposed and fully expanded leaves. Trees with lower gs Landscape Establishment, Adventitious Root Growth, and Rooting Potential of Shoot Cuttings for Platanus occidentalis Provenances Provenance differences in establishment of P. occidentalis as affected by root regeneration potential were studied under field and greenhouse conditions. Four half-sib families, two from Tex- as and one each from Tennessee and Kentucky, U.S., were studied (Shoemake 1996; Shoemake and Arnold 1997; Shoemake et al. 2004). The Kentucky selection was a superior provenance from the Westvaco Corporation and the Tennessee provenance was a mediocre performing selection identified in the previous studies. These were chosen as superior and average comparisons. Seedlings were transplanted to containers and grown under nursery condi- tions and subsequently transplanted to simulated landscape plots in the field (College Station, Texas) and root observation cham- bers under controlled conditions in a greenhouse, as described by Shoemake and Arnold (1997) and Shoemake et al. (2004). As a follow-up to these field studies, five P. occidentalis seed- lings from the best performing Texas (Texas 1) and the mediocre Tennessee provenances were randomly selected from the land- scape trials in the previous study. These were used as explant sources for shoot tip cuttings to determine if adventitious rooting from shoots followed similar patterns as the seedling’s root regen- eration potential from the same provenances. Cuttings from three developmental stages were compared in rooting percentages and various root quality measures, such as root number per cutting, root length, and dry mass. No root inducing growth regulators were applied so that rooting responses were those endogenous to the tissues. Forty cuttings from each of five seedlings (designated hereafter as clones 1 through 5) per provenance were placed in a greenhouse as softwood (late spring), semi-hardwood (mid-sum- mer), or hardwood (dormant tissue in winter) cuttings under in- termittent mist (6 sec. each 8 min.) from dawn to dusk in a green- house on 27°C day / 21°C night setpoints. Cuttings were rooted in 38 cm × 53 cm × 10 cm black plastic flats (Kadon Corp., Dayton, Ohio) containing screened (≤1.0 cm) composted pine bark chips. RESULTS AND DISCUSSION Taxodium distichum studies. Significant (P ≤ 0.05) location by clone interactions were present for all measured characteristics. In many locations T. distichum var. mexicanum accessions grew larger than the species type or those from Texas Hill Country
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