Arboriculture & Urban Forestry 33(6): November 2007 387 of the root ball (size of the root ball was 50 to 55 cm [20 to 22 in] in diameter). Trees were backfilled with: 1) topsoil with 25% composted material (volume/volume); 2) topsoil with 50% composted material; 3) topsoil with 75% composted material; or 4) top- soil only. Composted material was obtained from yard waste through aerobic biostabilization; compost was aerobic biosta- bilized with characteristics meeting the Italian standards (Table 1). After planting, the soil surface was covered with: 1) an “opus incertum” pavement (this technique uses irregularly shaped, small, smoothed slabs of stone randomly fitted to- gether with sealed joints) and a metal grate (1 × 1m[3.3 × 3.3 ft]); 2) left free of pavement for an area of 2.5 × 2.5 m (8.25 × 8.25 ft) around the trunk (6.25 m2 [67.5 ft2]), mulched with pine bark, and then planted with Viburnum davidii Franch. Trees were planted in a completely randomized block de- sign and regularly irrigated during spring and summer of each year. After the first year, some plants, regardless of the treat- ment, showed some dieback and were dropped from the mea- surements to obtain reliable data, measurements were per- formed on three single-plant replicates of four backfilling materials and six single replicates of planting area dimension. A CIRAS-1 portable infrared gas analyzer (PP Systems, Hert- fordshire, UK) was used to determine instantaneous net pho- tosynthesis (Pn), transpiration rate (E), and water use effi- ciency (WUE, calculated by dividing Pn by E) three times in the first and second year and five times in the third year (from mid-June through mid-August). Measurements of leaf gas exchange were started in mid-June. The readings were taken between 8:00 A.M. and 4:00 P.M. during sunny days (photo- synthetically active radiation greater than 1000 mol/m−2/ s−1) on ten fully expanded leaves from the outer part of the crown and at different heights per plant per treatment and repeated three times each day of measurements. Chlorophyll Table 1. Average composition (percent on dry matter) of the mixed compost added to the planting pit. Parameter Humidity pH Total nitrogen Organic carbon Organic matter C/N ratio Total phosphorus P2 O5 Potassium exchangeable K2 Plastic materials (less than 3.3 mm [0.13 in]) Total of inert material Value in organic compost used Limit values (according to Italian Legislation) 13.9% Maximum 50 6.3 6.0–8.5 1.95% — 26.1% Maximum 25 45% — 13.4 0.37% — O 1.00% — 0.3% Maximum 0.45 0.7% Maximum 0.9 Maximum 25 content was determined in July and September on the same leaves with a portable chlorophyll meter (SPAD-502; Minolta Corp., Ramsey, NJ, U.S.). Previous calibration curves were established for the species by measuring absorbance at 664, 647, and 625 nm with an Hitachi U-2000 spectrophotometer (Hitachi Ltd., Tokyo, Japan) after extraction with dimethyl- formamide (Moran 1982). Triplicate readings were taken around the midpoint near the midrib of each leaf sample and the values averaged. Dry weight was determined on ten leaves per plant per treatment. The leaves were chosen from the outer part of the crown at different heights with similar conditions of shape and weight. Leaves were dried at 80°C (176°F) until constant weight. In the second and third years of the experiment, leaves chosen from the same part of the tree were analyzed for mineral elements content by a specialized laboratory (MAC– Minoprio Analisi e Certificazioni). Effects of compost addition and of mulch and paving sur- face and significant interactions between compost addition and of mulch and paving surface were determined by one- and two-way analyses of variance. Differences between treat- ment means were separated by the protected least signifi- cance difference at the 95% confidence level (P 0.05). RESULTS AND DISCUSSION First Year The results from the first year indicate that the modification of the planting pit had no influence on leaf dry weight and leaf gas exchange. Only the transpiration rate was higher in the trees backfilled with topsoil +75% compost and in the control ones. No significant differences were found regarding leaf chlorophyll content either (Table 2). No statistical differences emerged regarding the size of the open soil surface with the exception of the WUE, which was higher in the trees that had mulch and groundcover planting. The interactions between the two factors showed statistical significance, although not univocal; this is most likely the effect of transplant shock. Second Year In the second year after transplanting, leaf dry weight and leaf gas exchanges were not affected by soil amendments. Chlo- rophyll content was lower in the trees amended with 25% of composted material (Table 3). The surface treatment had significant effects on all of the parameters measured. Trees growing with the pavement and grate had a lower leaf dry weight, reduced leaf gas exchange, and lower leaf chlorophyll content. These findings are similar to those of Celestian and Martin (2005) who compared four dif- ferent ornamental species in two parking lot locations in United States, finding, in general, a higher leaf gas exchange and leaf chlorophyll content in the trees with the larger landscape area. ©2007 International Society of Arboriculture
November 2007
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