Gross N transformations were little affected by 4 years of simulated N and S depositions in an aspen-white spruce dominated boreal forest in Alberta Canada

Cheng Y Cai ZC Zhang JB et al.. Gross N transformations were little affected by 4 years of simulated N and S depositions in an aspen-white spruce dominated boreal forest in Alberta Canada. Forest Ecology and Management 2011 262(3): 571-578. (IF 1.992 农林科学，二区Top）

Abstract

    The effects of 4 years of simulated nitrogen (N) and sulfur (S) depositions on gross N transformations in a boreal forest soil in the Athabasca oil sands region (AOSR) in Alberta Canada were investigated using the ¹⁵N pool dilution method. Gross NH₄⁺ transformation rates in the organic layer tended to decline (P < 0.10 marginal statistical significance same below) in the order of control (CK i.e. no N or S addition) +N (30 kg N ha⁻¹ yr⁻¹) +S (30 kg S ha⁻¹ yr⁻¹) and +NS treatments with an opposite trend in the mineral soil. Gross NH₄⁺ immobilization rates were generally higher than gross N mineralization rates across the treatments suggesting that the studied soil still had potential for microbial immobilization of NH₄⁺ even after 4 years of elevated levels of simulated N and S depositions. For both soil layers N addition tended to increase (P < 0.10) the gross nitrification and NO₃⁻ immobilization rates. In contrast S addition reduced (P < 0.001) and increased (P < 0.001) gross nitrification as well as tended (P < 0.10) to reduce and increase gross NO₃⁻ immobilization rates in the organic and mineral soils respectively. Gross nitrification and gross NO₃⁻ immobilization rates were tightly coupled in both soil layers. The combination of rapid NH₄⁺ cycling negligible net nitrification rates and the small NO₃⁻ pool size after 4 years of elevated N and S depositions observed here suggest that the risk of NO₃⁻ leaching would be low in the studied boreal forest soil consistent with N leaching measurements in other concurrent studies at the site that are reported elsewhere.