Details

Autor(en) / Beteiligte

• Groffman, Peter M.
• Driscoll, Charles T.
• Fahey, Timothy J.
• Hardy, Janet P.
• Fitzhugh, Ross D.
• Tierney, Geraldine L.

Titel

Effects of Mild Winter Freezing on Soil Nitrogen and Carbon Dynamics in a Northern Hardwood Forest

Ist Teil von

• Biogeochemistry, 2001-11, Vol.56 (2), p.191-213

Ort / Verlag

Heidelberg: Kluwer Academic Publishers

Erscheinungsjahr

2001

Quelle

Alma/SFX Local Collection

Beschreibungen/Notizen

• Overwinter and snowmelt processes are thought to be critical to controllers of nitrogen (N) cycling and retention in northern forests. However, there have been few measurements of basic N cycle processes (e.g. mineralization, nitrification, denitrification) during winter and little analysis of the influence of winter climate on growing season N dynamics. In this study, we manipulated snow cover to assess the effects of soil freezing on in situ rates of N mineralization, nitrification and soil respiration, denitrification (intact core, C2H2 - based method), microbial biomass C and N content and potential net N mineralization and nitrification in two sugar maple and two yellow birch stands with reference and snow manipulation treatment plots over a two year period at the Hubbard Brook Experimental Forest, New Hampshire, U.S.A. The snow manipulation treatment, which simulated the late development of snowpack as may occur in a warmer climate, induced mild (temperatures > -5 °C) soil freezing that lasted until snowmelt. The treatment caused significant increases in soil nitrate (NO3-) concentrations in sugar maple stands, but did not affect mineralization, nitrification, denitrification or microbial biomass, and had no significant effects in yellow birch stands. Annual N mineralization and nitrification rates varied significantly from year to year. Net mineralization increased from ∼ 12.0 g N m-2 y-1 in 1998 to ∼ 22 g N m-2 y-1 in 1999 and nitrification increased from ∼ 8 g N m-2 y-1 in 1998 to ∼ 13 g N m-2 y-1 in 1999. Denitrification rates ranged from 0 to 0.65 g N m-2 y-1. Our results suggest that mild soil freezing must increase soil NO3- levels by physical disruption of the soil ecosystem and not by direct stimulation of mineralization and nitrification. Physical disruption can increase fine root mortality, reduce plant N uptake and reduce competition for inorganic N, allowing soil NO3- levels to increase even with no increase in net mineralization or nitrification.