Soil moisture effects on gross nitrification differ between adjacent grassland and forested soils in central Alberta, Canada
Cheng, Yi | Cai, Zu-cong | Zhang, Jin-bo | Lang, Man | Mary, Bruno | Chang, Scott X.
BACKGROUND AND AIMS: Changes in soil moisture availability seasonally and as a result of climatic variability would influence soil nitrogen (N) cycling in different land use systems. This study aimed to understand mechanisms of soil moisture availability on gross N transformation rates. METHODS: A laboratory incubation experiment was conducted to evaluate the effects of soil moisture content (65 vs. 100% water holding capacity, WHC) on gross N transformation rates using the 15N tracing technique (calculated by the numerical model FLUAZ) in adjacent grassland and forest soils in central Alberta, Canada. RESULTS: Gross N mineralization and gross NH 4 + immobilization rates were not influenced by soil moisture content for both soils. Gross nitrification rates were greater at 100 than at 65% WHC only in the forest soil. Denitrification rates during the 9 days of incubation were 2.47 and 4.91 mg N kg-1 soil d-1 in the grassland and forest soils, respectively, at 100% WHC, but were not different from zero at 65% WHC. In the forest soil, both the ratio of gross nitrification to gross NH 4 + immobilization rates (N/IA) and cumulative N2O emission were lower in the 65 than in the 100% WHC treatment, while in the grassland soil, the N/IA ratio was similar between the two soil moisture content treatments but cumulative N2O emission was lower at 65% WHC. CONCLUSIONS: The effect of soil moisture content on gross nitrification rates differ between forest and grassland soils and decreasing soil moisture content from 100 to 65% WHC reduced N2O emissions in both soils.
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