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

Author:
Cheng, Yi, Cai, Zu-cong, Zhang, Jin-bo, Chang, Scott X.
Source:
Forest ecology and management 2011 v.262 no.3 pp. 571-578
ISSN:
0378-1127
Subject:
Picea, boreal forests, forest soils, leaching, mineral soils, mineralization, nitrification, nitrogen, oil sands, organic soils, risk, sulfur, Alberta
Abstract:
The effects of 4years 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 (30kgNha⁻¹yr⁻¹), +S (30kgSha⁻¹yr⁻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 4years 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 4years 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.
Agid:
478141