Soil and sugar maple response to 8 years of NH 4 NO 3 additions in a base-poor northern hardwood forest Jean-David Moore a,⇑ , Daniel Houle a,b a Direction de la recherche forestière, Ministère des Ressources naturelles, 2700 rue Einstein, Québec, QC G1P 3W8, Canada b Environment Canada, Science and Technology Branch, Montréal, QC, Canada article info Article history: Received 16 May 2013 Received in revised form 9 August 2013 Accepted 10 August 2013 Available online 11 September 2013 Keywords: Sugar maple Nutrition Nitrogen deposition Calcium nutrition abstract Ammonium nitrate was added annually at 3- and 10-fold the ambient wet atmospheric deposition rate (8.5 kg ha 1 year 1 ) during 8 years in a base-poor northern hardwood forest of Québec, Canada. Soil chemistry and foliar chemistry, crown dieback and basal area growth of sugar maple (Acer saccharum Marsh.) were measured after 8 years of treatments. Despite repeated N additions, N concentrations in all soil layers remained similar between treatments. However, the treatments significantly reduced exchangeable Ca, Mg, Mn and K compared to the untreated plots, at least for one of the top organic soil layers. The most significant and substantial differences were observed for Ca between the control and the high N treatment, with the L and the H layers showing decreases of 29% and 72%, respectively. Foliar Ca and Mn concentrations decreased with increasing levels of N addition, while foliar N increased. Foliar Ca in the high N treatment decreased by 79% compared to the control and reached 0.24%, the lowest foliar Ca concentration ever reported for sugar maple. No significant treatment effects were observed for dieback rate or basal area growth, although mean dieback rate of sugar maple in the high N treatment was 43% higher than in the control. Our results show that increased N deposition, even at relatively low rates, can strongly affect Ca nutrition of sugar maple at sites with low base cation saturation. This raises concerns about the sustainability of sugar maple in acidic, base-poor forest soils. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Since the early 1980s, decreasing vitality of sugar maple (Acer saccharum Marsh.) has been a major concern in poorly buffered soils of northeastern North America (Duchesne et al., 2002; Horsley et al., 2002; Gavin et al., 2008; Long et al., 2009; Watmough, 2010; Moore et al., 2012). Sugar maple is known to be very sensitive to soil acidity (Thornton et al., 1986; Ouimet et al., 1996). In survey plots in Vermont, Wilmot et al. (1995) observed a strong correla- tion between soil pH and sugar maple dieback. In addition, many studies on sugar maple dieback have suggested that base cation deficiency, and particularly Ca deficiency, was a cause of tree growth reduction and decline (Huggett et al., 2007; Long et al., 2009; Watmough, 2010). Moreover, the positive growth and vigor response of sugar maple to liming or Ca addition in base-poor northern hardwood stands has demonstrated that Ca deficiencies are involved in the decline of sugar maple at many sites (Wilmot et al., 1996; Huggett et al., 2007; Long et al., 2011; Moore et al., 2012). Many studies have suggested that acid deposition has acceler- ated the loss of available Ca from soils with a low acid-buffering capacity in northern hardwood stands (Houle et al., 1997; Likens et al., 1996; McLaughlin, 1998; Bailey et al., 2005; Long et al., 2009). Duchesne et al. (2002) showed that the appearance of the sugar maple decline phenomenon and the associated growth reduction can be related, at least in part, to soil acidification and acid deposition levels in Québec. SO 4 and NO 3 are the major anio- nic components of acid deposition. In recent decades, S emissions and deposition have decreased in northeastern North America (Driscoll et al., 2001; Houle et al., 2004), due to a series of regula- tions designed to reduce S emissions from power plants and vehi- cles (NADP, 1998). Similar regulations have also targeted N deposition (US EPA, 2010) and have resulted in significant reduc- tions in NO x emissions and deposition, both in the United States (US EPA, 2010; Pinder et al., 2011; Templer et al., 2012) and in Canada (Geddes et al., 2009). The same decreasing trend in NO x deposition has been observed in some areas of Québec (L. Duch- esne, unpublished data), including the study area. Unlike NO x emissions, NH 3 emissions are unlikely to decline, and an increasing trend has been reported in the United States (Templer et al., 2012). Thus overall, studies show that global atmospheric N deposition has doubled in the last one hundred years and is projected to more than double in the next century, mainly due to fossil fuel combus- tion and growing demand for N by agriculture and industry (Galloway et al., 2004, 2008). 0378-1127/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.foreco.2013.08.020 ⇑ Corresponding author. Tel.: +1 4186437994. E-mail address: jean-david.moore@mrn.gouv.qc.ca (J.-D. Moore). Forest Ecology and Management 310 (2013) 167–172 Contents lists available at ScienceDirect Forest Ecology and Management journal homepage: www.elsevier.com/locate/foreco