254 Atomic Energy Agency 1983) F = Grams of fertilizer The percentage of nitrogen derived from fertilizer (NDFF) was adapted from equations developed by Hauck and Bremner (1976). [Equation 2] NDFF = Where: A = 15 B = 15 C = 15 C D A B − − N % in fertilized tissue sample N % in tissue prior to fertilization N % in fertilizer D = Natural abundance of 15 N which is 0.366% Biomass weighted total N was calculated as follows: [Equation 3] Weighted TN = ∑ (% total biomass F, Sc, S × % TN F, Sc, S ) Where: F = foliage as a percent of total aboveground biomass (g) Sc = current season stem wood as a percent of total above- ground biomass (g) S = stem wood as a percent of total aboveground biomass (g) Treatment effects within a harvest period were determined using mixed model ANOVA procedures in SAS (Littell et al. 2004). Application rate was the fixed effect and treatment within a block was a random effect. Scatter plots of residuals versus predicted values and the Kolmogorov-Smirnov test were used to test assumptions of normality. The log likelihood test was used to select the appropriate analysis model. Statistical analysis on the percentage of NDFF was performed on arcsin square root transformed data because many of the data sets did not meet the assumption of equal variances. Comparisons of treatment effects were made using Fisher’s least significant difference test with P ≤ 0.05. References to percent changes resulting from increases in the rate of application are based upon back-transformed values. RESULTS AND DISCUSSION nei’) following defoliation by gypsy moth (Lymantria dispar L.). Additionally, foliar frost damage may have reduced root prolif- eration and growth within the Root Control™ bags. Root initiation Just prior to transplanting, a late spring frost did extensive dam- age to the foliage at Lisle, IL which resulted in a second flush of new foliage. Consequently, biomass partitioning (% of total aboveground dry weight) among the tissues was significantly dif- ferent between the study site locations 14, 30, and 60 days after treatment. The percentage of total aboveground biomass account- ed for by the foliage and current season stem wood at Arlington, WI was, on average, 84% and 78% higher than values observed at Lisle, IL during the 2002 growing season. The reduction in foliar biomass may have negatively affected fertilizer N acquisi- tion and recovery at Lisle, IL. Similar results were observed by Kosola et al. (2001) who reported reduced uptake of NO3 NH4 - and + in hybrid poplar (Populus × canadensis Moench. ‘Euge- and expansion requires a carbon (C) substrate, with the primary source being carbohydrates produced during photosynthesis with- in the leaves. The flush of new foliage may have resulted in a de- mand for N that occurred after the fertilizer application date and/or ©2009 International Society of Arboriculture Figure 1. Total [N] in foliage of common hackberry at (A) Arling- ton, WI and (B) Lisle, IL in 2002. Symbols represent the mean (n = 5) ± the adjusted standard error. Asterisk indicates signifi- cant difference at P ≤ 0.05. Werner and Jull: Fertilizer Uptake, Partitioning, and Recovery in Container-Grown Trees influenced carbohydrate allocation to the roots and subsequently, the capacity to acquire fertilizer N (Huett 1996; Kosola et al. 2001). Impact of Fertilization on Total N Concentration The rate of application significantly affected foliar total N con- centration [N] 60 days after treatment and was borderline signifi- cant (P = 0.052) at 30 days at Arlington, WI and 14 days after treatment at Lisle, IL (Table 1). At Arlington, WI, the 4.27 g N application rate increased foliar N by 57% and 11%, relative to control trees and trees receiving 1.42 g N, respectively, at 30 days after treatment (Figure 1). Similarly, increases of 20% and 9% were observed 60 days after fertilization in Arlington, WI for 4.27 g N application rate. At Lisle, IL, foliar N at 14 days after treat- ment was 20% and 11% higher in trees receiving the 4.27 g N application rate, relative to control trees and trees receiving 1.42 g N, respectively. Increases in foliar N concentration have been shown to improve short-term photosynthetic efficiency (g C fixed m-2 ) and net carbon assimilation, resulting in greater leaf area and enhanced aboveground biomass production (Gough et al. 2004). However, there is growing evidence to suggest there is a physi- ological threshold surrounding N accumulation in the foliage,
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