Nutrient cycling in Huntington Forest and Turkey Lakes deciduous stands: nitrogen and sulfur

Biogeochemical cycling of S and N was quantified at two hardwood sites (Turkey Lakes watershed (TLW) and Huntington Forest (HF)) that have sugar maple (Acersaccharum Marsh.) as the major overstory component and are underlain by Spodosols (Podzols). TLW and HF are located in central Ontario (Canada) and the Adirondack Mountains of New York (U.S.A), respectively. Major differences between the TLW and HF sites included stand age (300 and 100 years for TLW and HF, respectively), age of dominant trees (150-300 and 100 years for TLW and HF, respectively), and the presence of American beech (Fagusgrandifolia Ehrh.) at HF as well as lower inputs of SO 4 2− and NO 3 − (differences of 99 and 31 mol ion charge (mol c )*ha −1 *year −1 , respectively) at TLW. There was an increase in concentration of SO 4 2− and NO 3 − after passage through the canopy at both sites. A major difference in the anion chemistry of the soil solution between the sites was the much greater leaching of NO 3 − at TLW compared with HF (1300 versus 18 mol c *ha −1 *year −1 , respectively). At HF, but not TLW, there was a marked increase in SO 4 2− flux (217 mol c *ha −1 *year −1 ) when water leached from the forest floor through the mineral soil. The mineral soil was the largest pool (>80%) of N and S for both sites. The mineral soil of TLW had a C:N ratio of 16:1, which is much narrower than the 34:1 ratio at HF. This former ratio should favor accumulation of NH 4 4+ and NO 3 − and subsequent NO 3 − leaching. Laboratory measurements suggest that the forest floor of TLW may have higher N mineralization rates than HF. Fluxes of N and S within the vegetation were generally similar at both sites, except that net requirement of N at TLW was substantially lower (difference of 9.4 kg N*ha −1 *year −1 ). The higher NO 3 − leaching from TLW compared with HF may be attributed mostly to stand maturity coupled with tree mortality, but the absence of slow decomposing beech leaf litter and lower C:N ratio in the soil of the former site may also be contributing factors.