『Abstract
　It is commonly assumed that nitrogen (N) is the primary mineral resource limiting the productivity of temperate forests. Sustained inputs of N via atmospheric deposition are altering the N status of temperate forests raising the possibility that nutrients such as phosphorus (P) are increasingly limiting productivity. The objective of this study was to determine whether P availability limits tree growth alone or in combination with N. This study was conducted in two forest types common throughout the New England landscape of the northeastern United States; in sugar maple and white ash dominated stands growing on base rich parent material characterized by rapid rates of N cycling and high N availability, and in red oak-beech-hemlock dominated stands growing on base-poor parent material characterized by slow rates of N cycling and low N availability. Starting in 2004, N and P were added to replicate plots in each forest type in factorial combination at a rate of 150 and 50 kg ha^-1 year^-1, respectively. Diameter growth rates of all trees＞10 cm DBH were measured in 2005 and 2006 using dendrometer bands and converted into units of basal area increment (BAI) and wood production. Following 2 years of fertilization, basal area increment in the sugar maple-white ash forests remained strongly N limited. Fertilization with P did not significantly increase BAI alone, although both N and P fertilization tended (P＜0.10) to increase diameter growth in white ash. Wood production in the N-fertilized plots increased by 100 g C m^-2 year^-1, roughly doubling production in the non-fertilized plots. In the red oak-beech-hemlock stands, there was no overall effect of N or P fertilization on BAI or wood production because BAI in some species was stimulated by fertilization with N alone (e.g., black cherry, red oak), while in other species BAI was unaffected (e.g., red maple, beech) or negatively affected by fertilization with N or P (e.g., eastern hemlock). Given that BAI in several tree species responded to fertilization with N alone and that only one species responded to P fertilization once N was added, this study suggests that decades of atmospheric N deposition have not (yet) resulted in widespread P limitation or saturation of tree demand for N.

Keywords: Nitrogen; Phosphorus; Temperate forest; Nutrient limitation; Productivity

Introduction
Methods and materials
　Study site
　Foliage sampling
　Soil sampling
　N and P fertilization experiment
　Data analysis
Results
　Foliar and litter N and P
　Soil N and P
　N and P fertilization experiment
Discussion
Conclusion
Acknowledgments
Appendix
References