258 Werner and Jull: Fertilizer Uptake, Partitioning, and Recovery in Container-Grown Trees The percent NDFF in the current season stem wood of trees receiving the 1.42 g N application rate nearly mirrored the trends in foliar NDFF at both locations. At Arlington, WI, maximum NDFF in current season stem wood occurred 30 days after treatment in trees receiving 1.42 g N or 4.27 g N, 7.7% and 20.9%, respectively. At Lisle, IL, maximum current sea- son stem wood NDFF occurred at 14 days after treatment at both rates of application. Additionally, at Lisle, IL, the percent NDFF in current season stem wood of trees receiving 4.27 g N increased by 19.1% between 60 and 90 days after treatment. In stem wood, maximum percent NDFF for trees receiving the 4.27 g N treatment occurred 90 days after fertilization at Ar- lington, WI (13.7%), and Lisle, IL (5.4%). Relative to values at 14 days, the percent NDFF in stem wood at 90 days in trees re- ceiving 4.27 g N increased by 125% and 25% at Arlington, WI and Lisle, IL, respectively. Maximum NDFF in the stem wood of trees receiving 1.42 g N occurred at 90 days (4.5%) and 60 days (1.4%) after treatment at Arlington, WI and Lisle, IL, re- spectively. Between 14 and 90 days after treatment, the per- cent NDFF in stem wood increased by 10% at Arlington, WI. There was little change (1.2% versus 1.3%) in the percent NDFF in stem wood at Lisle, IL between these two harvest periods. The maximum percent NDFF in root tissues of trees receiv- ing 1.42 g N occurred 60 days after treatment at Arlington, WI and Lisle, IL, 7.3% and 2.8%, respectively (Table 3). Maximum values for trees receiving 4.27 g N occurred at 30 days in Arling- ton, WI (18.6%), and at 90 days in Lisle, IL (6.9%). Throughout the remaining harvest periods, root NDFF remained fairly con- stant at Arlington, WI. However, between 30 and 60 days after treatment, root NDFF at Lisle, IL increased by 70% and 34% in trees receiving the 1.42 g N and 4.27 g N treatments, respectively. The combination of increases in the percent NDFF in stem wood, particularly in the 4.27 g N treatment level and declines in the percent NDFF in foliage at 90 days is consistent with theo- ries of N conservation in higher plants growing in an N limited environment. Research found approximately 50% of foliar N is removed prior to abscission and subsequently stored as low mo- lecular weight proteins in stem and root tissues (Chapin and Ked- rowski 1983; Aerts 1996). Data from this study indicate increasing rates of application consistently enhances fertilizer N accumula- tion in the foliage. However, the amount of fertilizer N removed from the foliage during leaf senescence is not consistent across the treatment levels. Relative to maximum values observed dur- ing the growing season (14–60 days after treatment), the percent NDFF in the foliage of trees receiving 4.27 g N declined by 27% at 90 days after treatment in both locations. In contrast, foliar NDFF at 90 days in trees receiving the 1.42 g N rate of application was 44% lower than maximum growing season values at Arlington, WI, and 58% lower at Lisle, IL. However, at both locations and across the treatment levels, there were consistent declines in fo- liar total [N]. Consequently, these data suggest trees receiving the high rate of application tended to lose more fertilizer N in the leaf litter. The fertilizer N contained within the leaf litter likely con- sists of structural proteins associated with new growth or photo- synthetic proteins trapped in the foliage when the abscission layer was activated (Escudero and Mediavilla 2003; Hoch et al. 2003). These findings support Aerts (1996) conclusion that increasing the level of available N would either suppress or have no effect upon the amount of N removed from leaves prior to senescence. At both locations and rates of application, 61%–78% of the fertilizer N that accumulated in aboveground tissues was parti- tioned to the foliage 14, 30, and 60 days after fertilization (Table 5). At 90 days after treatment, the percentage of aboveground fertilizer N accumulation in the foliage declined substantially in both treatment levels and locations. These reductions, particu- larly at 90 days after treatment, may be attributed to leaf loss and the onset of leaf senescence. Declines in the foliar contri- bution to aboveground fertilizer N accumulation coincided with increases in fertilizer N accumulation in stem wood in all treat- ment combinations at both locations and all rates of application. These observations are consistent with patterns of internal N cycling and storage (Brinkman and Boerner 1994; Aerts 1996). Fertilizer Recovery (% of N Applied) The inability to consistently separate root tissues from the rooting medium prevented the determination of fertilizer N recovery in the root system. As a result, fertilizer N recovery is presented only for the aboveground tissues. Within both locations, there were no significant differences in the percentage of fertilizer N recovered between the 1.42 g N and 4.27 g N application rates in any of the harvest periods (Table 2). Pre-senescent (before 90 days after treatment), back-transformed, recovery rates in aboveground tis- sues ranged from 15%–25% at Arlington, WI, and 5%–10% at Lisle, IL (Figure 4). While reported, the extent of leaf senescence and loss at 90 days after treatment, particularly at Arlington, WI, prevented a meaningful interpretation of fertilizer N recovery. At Arlington, WI, maximum recovery rates occurred at 30 days for the 1.42 g N treatment (22.3%) and at 60 days for the 4.27 g N treatment (25.1%). At Lisle, IL, maximum recovery rates for trees receiving the 1.42 g N and 4.27 g N application rates oc- curred 30 days after fertilization, 9.4% and 7.7%, respectively. The range of recovery rates for both treatments at Arlington, WI were slightly higher than fertilizer N recovered in a lodge- pole pine (Pinus contorta Dougl. ex Loud.) (Preston and Mead 1994) and black spruce [Picea mariana (Mill.) BSP] (Salifu and Timmer 2003), comparable to fertilizer recovery rates ob- served in pecan [Carya illinoinensis (Wangenh.) K. Koch] Table 5. Percent applied fertilizer N partitioned to aboveground common hackberry tissues at Arlington, WI, and Lisle, IL in 2002. Arlington, WI Lisle, IL Tissue Foliage Current Stem Wood Stem Wood Foliage Current Stem Wood Stem z Values are means of n = 5. Trt (g) 1.42 1.42 1.42 4.27 4.27 4.27 14 11.4z 0.8 3.4 10.9 0.8 3.1 Days after Fertilization 30 60 15.7 0.9 6.0 17.4 0.9 6.4 13.2 1.0 7.6 15.2 1.0 8.7 90 1.3 0.1 8.4 0.7 1.1 9.2 14 5.8 0.5 1.3 4.8 0.6 1.6 Days after Fertilization 30 60 6.2 0.5 1.2 6.0 0.5 1.6 3.4 0.3 1.4 3.4 0.3 1.8 90 1.5 0.2 2.2 2.2 0.4 2.9 ©2009 International Society of Arboriculture
September 2009
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