Arboriculture & Urban Forestry 32(3): May 2006 97 Treatment Control Table 7. Effect of fertilization on leaf mineral content (%) of Liquidambar styraciflua L. trees. 2002 P 2003 N 1 Fertilization 2 Fertilization 2.95 a* 3.15 a 3.06 a 0.12 a 0.14 a 0.11 a K 0.48 a 0.81 a 0.60 a N 2.22 a 2.24 a 2.37 a *Values differ significantly when followed by different letters at P 0.05 (LSD test). which showed a significant reduction of leaf gas exchanges in the third year after planting. Chlorophyll Content Control plants had less total chlorophyll than the fertilized ones in the first 2 years after planting, while in the third year no differences were found among the different treatments (Table 6). Leaf Mineral Content No significant effect of fertilization on leaf mineral content as a percentage of dry weight was found in the first 2 years, but in the third year fertilized trees showed a higher nitrogen and potassium content (Table 7). Plant Growth No effects on shoot growth and leaf dry weight were ob- served in the first 2 years, but in 2004 shoots were signifi- cantly longer in the control trees (data not shown). Since fertilization led to neither an increase in the leaf content or an increase in shoot growth, it seems that the plants have not taken up different amounts of fertilizer. This might be due to the fact that transplanting often leads to a measur- able, long-term water stress that cannot be easily relieved even using fertilization and watering in combination. In ad- dition, trees from the nursery have a decreased root system that can be less capable of acquiring nutrients, leading to no effect on growth and leaf concentrations even with increased fertilization. CONCLUSIONS During the 3-year experiments, the application of fertilizer showed contrasting effects on tree growth and leaf gas ex- change. Although we found some differences, they were lim- ited to 1 year, and only to some parameters. Contrary to findings in a previous paper on oak fertilization (Ferrini et al. 2005) the results of this research do not support the utility of fertilizer application as a method to improve plant establish- ment, growth, and physiology after transplanting in the urban environment. This may be due to the different conditions in which the experiments were conducted: oak trees were stud- ied in an urban park; and ash, Japanese pagoda, and sweet- gum trees were studied in a crowded street and in a parking lot. However, research carried out on Ilex rotunda showed that the photosynthetic rate of the trees was higher in urban areas than in suburban areas (Takagi and Gyokusen 2004). Carrying out experiments in the urban environment is often demanding because the variations between neighboring areas may be considerable. Therefore, there are probably other rea- sons why fertilization may not have affected tree growth and physiology (e.g., climate conditions, changes in soil physical conditions after planting, the presence or absence of main- tained turfgrass), so it is difficult to make specific recom- mendations about tree fertilization in urban sites. Urban for- est managers should be aware of this before deciding whether fertilization is appropriate or cost-effective after planting trees in urban stands. Acknowledgments. Support for this project came in part from the Regione Toscana (Italy) as part of the research project “Research on Multipurpose Green Areas” (RISVEM). A special thanks to the Parks and Gardens Service of Milano Town Council for the techni- cal support to the research. LITERATURE CITED Bradshaw, A., B. Hunt, and T. Walmsley. 1995. The need for nutrients, pp. 157–169. Trees in the urban landscape. E.&F.N. Spon, London. Brix, H., and A.K. Mitchell. 1986. Thinning and nitrogen fertilization effects on soil and tree water stress in a Douglas-fir. Canadian Journal of Forest Research 16: 1334–1338. Ferrini, F., A. Giuntoli, F.P. Nicese, S. Pellegrini, and N. Vignozzi. 2005. Effect of fertilization and backfill amend- ments on soil characteristics, growth and leaf gas ex- changes of English oak (Quercus robur L.). Journal of Arboriculture 31(4):182–190. Foster, C.M., H.T. Horner, and W.R. Graves. 2000. Accu- mulation of ENOD2-like transcripts in non-nodulating woody papilionoid legumes. Plant Physiology 124: 741–750. Gilman, E.F. 1987. Response of hibiscus to soil-applied ni- trogen. Proceedings of the Florida State Horticultural So- ciety 100:356–357. Gilman, E.F., T.H. Yeager, and D. Kent. 2000. Fertilizer rate and type impacts magnolia and oak growth in sandy land- scape soil. Journal of Arboriculture 26(3):177–182. ©2006 International Society of Arboriculture P 0.06 a 0.13 a 0.16 a K 0.57 a 0.82 a 0.59 a N 2.21 b 2.61 a 2.49 a 2004 P 0.07 a 0.07 a 0.08 a K 0.25 b 0.57 a 0.58 a
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