Chemistry of soil and foliage in declining sugar maple stands over 13 years of nitrogen addition.

• Cumulative impact of atmospheric nitrogen (N) deposition is a concern for forest ecosystems. • N doses (0, 3, 10 times ambient rate) were applied during a 13-year period in a sugar maple stand. • N concentrations in foliage and organic soil remained similar between treatments after 13 years. • Soil nitrate increased and Ca, Mg, and K (top organic layers) decreased in the high N treatment. • Foliar N:P ratio increased while Ca and Mn decreased with increasing levels of N addition. • Sugar maple dieback rate increased over time in the high N treatment. Cumulative effects of nitrogen (N) deposition are a matter of concern in temperate forests of northeastern North America. Increased N deposition may stimulate forest growth and carbon sequestration while also causing N saturation, which may lead to soil cation depletion, particularly in base-poor systems. We applied ammonium nitrate for 13 years in a sugar maple (Acer saccharum; SM) stand at the rates of 3 (Low N, LN) and 10 times (High N, HN) the ambient N deposition rate. N concentrations in soil layers were similar among treatments, except for a nitrate increase in the top B horizon in the HN treatment. Exchangeable Ca²⁺, Mg²⁺, and K⁺ were significantly lower than for the Control, at least in one of the top organic soil layers in the HN treatment. The temporal dynamics of foliar chemistry revealed that N:P ratio increased and both Ca and Mn decreased in the early years following treatment initiation, but that they did not change much thereafter. Foliar Ca values in the HN treatment are the lowest reported in the literature. This probably explains why the proportion of crown dieback steadily increased over time, reaching values as high as 80% in the HN treatment in 2017. [ABSTRACT FROM AUTHOR]