Overwinter soil nitrogen dynamics in seasonally frozen soils

Abstract

An overwinter soil-monitoring study was conducted at two sites in southern Ontario. Soluble soil N accumulation at both sites occured in early winter, peaked when soil water was frozen, and then declined during the period that frozen soil water was present. The amount of soluble soil N accumulated was 48 ± 12 kg N ha−1 at one site, and 21 ± 6 kg N ha−1 at the other. In both cases, the overwinter accumulation approximately doubled the amount of soluble N in the soil. Similar trends were observed in both mineral and organic N, with 60 to 74% of the accumulation occurring in the organic form. No clear correlations between soluble nitrogen dynamics and soil extractable organic carbon or soil microbial biomass carbon dynamics were observed. Denitrification apparently occurred in shallow soil during the thaw period at one site. Since soil nitrate levels decreased before significant thawing occurred, leaching was probably not the primary dissipation mechanism. We hypothesize that the soluble N accumulation was due to death and lysis of soil microorganims during freezing and thawing. The presence of soil ice apparently decreased the lethality of the soil enviroment, allowing N dissipation to occur. Soil N dissipation could be due to gaseous losses, and is likely related to significant N2O fluxes commonly observed during spring thaw. Key words: Nitrogen, overwinter, soil ice

The effect of soil freezing on N cycling: comparison of two headwater subcatchments with different vegetation and snowpack conditions in the northern Hokkaido Island of Japan

“…According to several laboratory studies, when soils freeze, root and microbial mortality results in a release of labile organic carbon (C) and nitrogen (N) to soil (Edwards and Cresser 1992;Schimel and Clein 1996;GroVman et al 2001a;Neilsen et al 2001) similar to what has been observed during wetting and drying cycles of soils (Birch 1958;Soulides and Allison 1961;Lund and Goksøyr 1980;Marumoto et al 1982;Kieft et al 1987;Davidson et al 1998). The majority of the initial released organic N and C upon thawing comes from cellular material released from death and lysis of microbial biomass (in the form of simple sugars and amino acids) rather than a release from disrupted organic structure (Schimel and Clein 1996;Ryan et al 2000;Hermann and Witter 2002). Increased net mineralization and nitriWcation occur during thawing as surviving organisms use the killed cells as a substrate (DeLuca et al 1992;Neilsen et al 2001) resulting in increased leaching of NO 3 ¡ to surface waters (Callesen et al 2007).…”

Modelling impacts of climate and deposition changes on nitrogen fluxes in northern catchments of Norway and Finland

“…Several studies have indicated very high, episodic rates of mineralisation, nitrification and denitrification associated with such periods (e.g. Goodroad and Keeney, 1984;Ryan et al, 2000).…”

Nitrogen dynamics in runoff from two small heathland catchments representing opposite extremes with respect to climate and N deposition in Norway

“…With air temperatures largely fluctuating around 0 o C during winter, the upper soil horizons will undergo frequent freezing/ thawing that may affect plant roots and soil organic matter and increase the substratum available for mineralisation (Monteith et al, 2000). In turn, this may lead to increased nitrification, reduced plant uptake and occasionally also increased denitrification (Ryan et al, 2000). The net effect, however, is often increased N leaching to surface waters (Mitchell et al, 1996;Monteith et al, 2000).…”