Arboriculture & Urban Forestry 40(6): November 2014 and analyzed colorimetrically at 882 nm on a spec- trophotometer (Model UV mini 1240, Shidmadzu Inc., Kyoto, Japan) (Olsen and Sommers 1982). Total carbon (C) and nitrogen (N) were determined by automated dry combustion on a CN analyzer (Vario ELIII, Elementar Analysensysteme, Hanau, Germany) (Nelson and Sommers 1996). Loss on ignition at 360°C for six hours was used to deter- mine the soil organic matter (SOM) content (Nelson and Sommers 1996). Microbial respiration (RES) was measured in 10 day dark incubations at 25°C with soils adjusted to 40% water-holding capacity with 0.25 M NaOH traps. Carbon dioxide seques- tered in NaOH was precipitated with 0.5 M BaCl2 followed by 0.25 M HCl (standardized) titration to a phenolphthalein endpoint (Parkin et al. 1996). Tree Biomass Sixty trees were destructively sampled in spring of 2011 and the remaining sixty in the spring of 2013. During each sampling period, five blocks of 12 trees each were sampled, with each block containing the full complement of treatments and species combi- nations. The sampling period did not interact with the main effects of treatment or species for any of the biomass fractions; consequently growth is pre- sented by combining data across the two sampling dates. For simplicity, change in tree biomass is pre- sented as growth aſter five years of treatment even though sixty trees had four years of treatments and sixty trees had six years of treatments (Figure 1). Trees were removed from the ground using a 0.9 m diameter tree spade (Optimal 880, Optimal-Vertrieb Optiz GmbH, Eysoelden, Germany) mounted on a multi terrain loader (Caterpillar 277B, Caterpillar Inc., Peoria, Illinois, U.S.). Soil was removed from rootballs using a pneumatic air tool (X-ST, Super- sonic Air Knife, Inc., Allison Park, Pennsylvania, U.S.). Turf roots were removed by hand-sorting. Tree biomass fractions of fine roots (<2 mm diameter), medium roots (2–5 mm), coarse roots (>5 mm), stems and leaves were hand-sorted, washed, dried to constant moisture (60°C for one week), and weighed. Statistical Analyses The experiment was a randomized complete block design, with 120 total plots, two species, six treat- ments and ten replications. Data distributions were checked for normality using the Shapiro- Figure 1. Stem, leaf, coarse, medium, and fine root biomass fractions of Acer rubrum and Betula nigra on a compacted urban soil plot receiving water control (NULL), commer- cial biological product (CBP), aerated compost tea (ACT), NPK fertilizer (FERT), wood chip mulch (WC), and compost (COMP) treatments for five consecutive years. Uppercase letters on top indicate significant differences among treat- ments in total biomass using Tukey’s HSD test. Lowercase letters indicate differences among leaf, stem, and coarse root fractions. Differences were not significant for medium and fine root fractions. Each fraction is a mean of 20 trees. Wilk W-test. Transformations of non-normal data were performed when necessary. Main effects and interactions were assessed with two-way repeated measures analysis of variance (ANOVA). Mean separations were carried out with the Tukey’s HSD test. Pairwise correlations with Pearson product- moment were used to identify significant rela- tionships among variables. Principal component analyses were used to establish which soil property explained most variance in the complete data set (Fox and Metla 2005). Significant differences were determined at the 95% confidence level. Statisti- cal analyses were conducted using SAS JMP 7.0 soſtware (SAS Inc., Cary, North Carolina, U.S.). RESULTS AND DISCUSSION Soil Responses All soil responses assessed in this research showed significant treatment effects and only microbial respiration (RES) showed a significant response ©2014 International Society of Arboriculture 323
November 2014
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