88 Werner and Jull: Fertilizer Uptake and Partitioning in Young and Mature Common Hackberry Significant interactions between growth phase and the rate of application were observed in 3 of the 19 (16%) potential sam- pling combinations (Table 1). Main effect interactions were observed in root tissues at 60 and 150 days after fertilization and at 14 days in the foliage. Within the root tissues, the rate of appli- cation affected total % [N] in both growth phases; while growth phase differences were only observed within TRT 2 (data not shown). During both harvest periods, root total % [N] in mature trees receiving TRT 2 were 13%–33% and 17%–40% higher than values observed in TRT 1 and TRT 3, respectively. In young trees, TRT 3 produced root total % [N] values that were 15%–40% higher than those observed in TRT 2 and TRT 1. In the foliage, growth phase differences at 14 days were apparent in TRT 1 (P = 0.011) and TRT 2 (P = 0.023), while the rate of application was significant only in the young growth phase (P = 0.026). In TRT 1 and TRT 2, foliar total % [N] in mature trees was 37%–69% higher than corresponding values in young trees. Total % [N] in the foliage of young trees receiving TRT 3 was 14% and 15% higher than values observed in TRT 1 and TRT 2, respectively. Throughout the growing season and up to the initia- tion of leaf senescence (90 days), the ranking of % total [N] by tissue type was: foliage ≥ fruit > current season stem wood > roots > stem wood. This trend occurred was observed in both growth phases and across all N levels. NDFF The main effect of growth phase on NDFF was significant in 13 of 19 (68.4%) potential sampling combinations (6 harvest periods × 4 tissue types, excluding tissue types or harvest periods in which a sample was not obtained) (Table 2). Significant differences were observed in all tissues common to both growth phases. In every instance the percentage of NDFF was substantially greater in young trees, in some cases by as much as 300% (i.e., stem wood, Figure 3). NDFF tended to increase rapidly through 30 days in all tissues within a growth phase and then stabilized between 60 and 90 days after fertilization. For example, the percentage of NDFF in the foliage of both young and mature trees at the time of leaf senescence (120 or 150 days) was not significantly dif- ferent than values observed at 30 days, P < 0.05 in all instances. The main effect of application rate was significant in 17 of 24 (70.8%) potential sampling combinations (6 harvest periods × 5 tis- sue types, excluding tissue types or harvest periods in which a sam- ple was not obtained) and occurred in all tissue types (Table 2). In every harvest period, NDFF was substantially higher in the tissues of trees receiving TRT 3 (Figure 4). Generally, the magnitude of increase in the percentage of NDFF was not proportional to the three- fold increase in the rate of application between TRT 2 and TRT 3. In the foliage, current season stem wood, stem wood, and roots the per- centage of back-transformed NDFF for trees receiving TRT 3 were 1.8, 1.6, 1.8, and 1.9 times higher, respectively, than same tissues in trees receiving TRT 2. Within the fruit, the increase in NDFF associ- ated with TRT 3 was 3.6 times higher than TRT 2 (data not shown). Interactions between growth phase and the rate of applica- tion had significant effects on the percentage of NDFF in 6 of 19 (31.6%) potential sampling combinations (6 harvest periods × 4 tissue types, excluding tissues or sampling dates that were not obtained) (Table 2). The interactions occurred only in the current season stem wood and stem wood. Within these harvest periods, the rate of application increased NDFF in the stem tissues within both; however, the magnitude of increase in response to the increasing N availability was greater in young trees. For example, NDFF in the current season stem wood increased, on average, by 130% and 250% in mature and young trees, respectively (data not shown). In young trees, the percentage of NDFF by tissue type was foliage > current season stem wood > roots > stem wood. In mature trees the percentage of NDFF by tissue type was fruit ≥ foliage > current season stem wood > root > stem wood. DISCUSSION Nitrogen, regardless of its source, is preferentially allocated to actively growing and/or photosynthetic tissues (Neilsen et al. 1997; Weinbaum and Van Kessel 1998; Rose and Biernacka 1999; Mattos et al. 2003; Werner and Jull 2008). The higher con- centrations of total % [N] in those tissues developed during the 2001 growing season in both growth phases and across all rates of application validate this fact. In deciduous trees, especially those displaying an indeterminate growth pattern, many of the high N tissues formed during the current growing season do not Table 1. Analysis of Variance (ANOVA) of the effect of growth phase and application rate on percent % total [N] in common hackberry tissues in 2001. Tissue Foliage Source Growth phase (GP) Treatment (Trt) GP * Trt Current stem wood Growth phase (GP) Treatment (Trt) GP * Trt Stem wood Roots Fruit Growth phase (GP) Treatment (Trt) GP * Trt Growth phase (GP) Treatment (Trt) GP * Trt Treatment z Leaves of young trees and fruit of mature trees not present at 150 days. y Tissues not collected at 30 days because of stress to canopy development in young trees. ©2013 International Society of Arboriculture Days after fertilization Pre 0.082 <0.001 0.759 0.587 14 0.028 0.277 0.040 <0.001 0.802 0.597 0.048 0.690 0.478 0.253 0.379 0.212 0.079 30 0.096 0.073 0.451 0.061 0.498 0.229 0.589 0.041 0.671 NAy NA NA 0.903 60 0.257 0.046 0.508 0.008 0.933 0.086 0.031 0.245 0.997 0.143 0.019 0.002 0.357 90 0.146 0.052 0.133 0.223 0.674 0.053 0.029 0.647 0.902 0.037 0.370 0.054 0.500 120 0.154 0.363 0.384 0.372 0.130 0.803 <0.001 0.066 0.191 0.039 0.003 0.416 0.226 150 NAz 0.869 NA <0.001 0.229 0.756 0.044 0.823 0.407 0.068 0.022 0.026 NAz
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