Litter decomposition and nutrient dynamics in oak–hickory forests along a historic gradient of nitrogen and sulfur deposition

White oak (Quercus alba L.) leaf litter decomposition rates and patterns of N, S and P immobilization and release in decomposing litter were quantified in oak–hickory forests in the Ohio river valley along a long-term (several decades) bulk atmospheric deposition gradient from Illinois, Indiana to Ohio. Historical data on deposition patterns between 1956–1985 showed that 30-y cumulative annual total (wet+dry) SO4–S concentrations were 19.9, 20.8 and 23.9 kg ha−1 y−1 and total (wet+dry) N concentrations were 5.99, 6.57 and 7.50 kg ha−1 y−1 in Illinois, Indiana and Ohio, respectively. In 1988–1989, amounts of total dry N deposition in Illinois, Indiana and Ohio were, respectively 2.71, 3.21, and 3.88 kg ha−1 y−1. Annual decay rates based on 19 months of decomposition data increased (p<0.05) with increased N deposition and were −0.294, −0.480, and −0.720, respectively. The decay rates correlated highly with both the total N concentration in the forest floor (r2=0.869, p<0.0001) and the amount of total dry N deposition (r2=0.999, p=0.007). Nitrogen mineralization from the litter was highest in Ohio and lowest in Illinois. Immobilization of S and P occurred only in Illinois. Litter at both the Ohio and Indiana sites showed a net mineralization of S and P but the rates were higher in Ohio. The results of the study suggest that atmospheric N inputs can affect litter decomposition and nutrient mineralization in oak–hickory forests in the lower Midwestern United States.