Journal of Arboriculture 31(6): November 2005 297 criteria: (1) presence of recently transplanted red maples in the landscape, and (2) proximity to a native forest contain- ing red maples. Red maple was chosen for observation due to its prevalence in both native forests and urban land- scapes and its capacity to form AMF symbioses. Native soils of the upper South Carolina Piedmont are ultisols of the Cecil series. Their taxonomic class is fine, kaolinitic, thermic Typic Kanhapludults (Soil Survey Staff 2005). Forested sites typically possess a thin (0 to 8 cm [0 to 3 in.]) organic horizon composed of partially decayed leaves and twigs. Upper mineral horizons are designated A, E, BE, and Bt1 to a depth of 71 cm (28 in.). This horizonation may be truncated due to erosion from past agricultural use, and one or more of the surface horizons may be absent. The A and B horizons are typically sandy loam, clay loam, or clay, and are moderately to very strongly acid. All of the commercial landscapes in our study had been established within the previous 3 years. The trees were typically established in highly disturbed native soil that had been graded and compacted to meet landscape design requirements. The surface soil was typically clay, and all trees possessed organic mulch rings to the drip line or beyond. The landscape maples had been balled and burlapped prior to transplant and were situated in parking lot islands or lawns near parking lot perimeters. Supplemental irrigation was present on some sites, but there was no known history of fertilizer or pesticide application to the trees. The average stem diameter of the landscape maples was 8.06 ± 0.79 cm (3.17 ± 0.31 in.) at the time of observation. The adjacent forest sites were typical midsuccessional mesic forests of the upper Piedmont. The overstory gener- ally consisted of white oak (Quercus alba), tulip poplar (Liriodendron tulipifera), and pignut hickory (Carya glabra). Flowering dogwood (Cornus florida), sweetgum (Liquidambar styraciflua), and red maple were common in the understory and midstory. White oak and hickory species are ectomy- corrhizal (Brundrett et al. 1990), while tulip poplar, sweetgum, flowering dogwood, and red maple form AMF symbioses (Simmons and Pope 1988; Klingeman et al. 2002). The surface soil at the forest sites was clay or clay loam and was covered with a thin duff mull litter layer. Each of the 18 sampling locations (nine paired landscape and forested locations) constituted an experimental unit within a randomized complete block design. Each commer- cial/retail establishment with its associated forested area constituted a block. Three maples were randomly selected as subsamples within each of the 18 experimental units. From each tree, fine roots were collected for AMF coloniza- tion measurement, soil was collected for chemical analysis and AMF inoculum potential measurement, and foliage was collected for tissue nutrient concentration measurement. For the landscape maples, mulch and surface soil were raked away from the root zone to permit identification of the root ball/bulk soil interface. To sample fine roots that had been produced after transplanting, three 20 cm (8 in.) deep soil cores were removed just outside the root ball at a 30 to 40 cm (12 to 16 in.) distance from the stem base. Cores were located 120 degrees apart around the root ball circumference. Three soil cores per tree were combined in a plastic bag and stored in a cooler. Approximately 100 g (3.5 oz) of young, fully expanded leaves were collected from the crown of each tree and stored in paper bags. At each forested location, three understory or midstory red maples were randomly selected as subsamples. Around the base of each tree, the litter layer was raked away to expose the mineral topsoil. To ensure that only red maple roots were collected, several lateral roots on each maple were manually excavated and approximately 2 g (0.07 oz) of live fine roots were harvested and stored in a cooler. Three 20 cm (8 in.) deep soil cores were collected around the circumfer- ence of each tree at a distance of about 30 cm (12 in.) from the stem base, combined in a plastic bag, and stored in a cooler. Foliage was sampled as in the landscape trees. Foliar samples were immediately oven-dried at 70°C (158°F) and submitted to the Clemson University Agricul- ture Service Laboratory for nutrient analysis. Root and soil samples were stored at 5°C (41°F) for less than 1 week before processing. Individual soil samples were passed through a 0.5 cm (0.2 in.) sieve to remove rock fragments and coarse woody debris. Coarse roots captured on the sieve were cut into 1 cm (2.5 in.) fragments and returned to the sieved soil. A 500 mL (17 fl oz) aliquot from each sieved soil sample was submitted to the Clemson University Agriculture Service Laboratory for nutrient analysis. The remaining sieved soil was returned to cold storage for 1 week prior to commenc- ing the greenhouse bioassay. Two grams (0.07 oz) of maple fine roots were removed from each landscape soil sample prior to sieving and stored at 5°C (41°F) in 50% ethanol. Forest maple fine roots were also stored in ethanol. Fine root samples were prepared for AMF assessment by rinsing with distilled water, clearing with 10% KOH for 6 to 12 h at 75°C (167°F), staining with trypan blue for 30 min at 75°C (167°F), and de-staining in 50% glycerol (Koske and Gemma 1989). AMF colonization was assessed using the magnified intersections method (McGonigle et al. 1990). For each sample, fifty 1 cm (0.4 in.) root segments were mounted on a glass slide and observed under 110x magnification using a compound microscope equipped with an cross-hair eyepiece. At a single intersec- tion between each root segment and the eyepiece cross-hair, the presence/absence of AMF hyphae was noted. AMF colonization was then calculated as the percentage of the 50 root segment intersections at which hyphae were present. A greenhouse bioassay was conducted to assess the AMF inoculum potential of soil from the landscape and forest ©2005 International Society of Arboriculture
November 2005
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