Snow depth, soil freezing and nitrogen cycling in a northern hardwood forest landscape

Abstract

Increases in soil freezing associated with decreases in snow cover have been identified as a significant disturbance to nitrogen (N) cycling in northern hardwood forests. We created a range of soil freezing intensity through snow manipulation experiments along an elevation gradient at the Hubbard Brook Experimental Forest (HBEF) in the White Mountains, NH USA in order to improve understanding of the factors regulating freeze effects on nitrate (NO 3 -) leaching, nitrous oxide (N 2 O) flux, potential and in situ net N mineralization and nitrification, microbial biomass carbon (C) and N content and respiration, and denitrification. While the snow manipulation treatment produced deep and persistent soil freezing at all sites, effects on hydrologic and gaseous losses of N were less than expected and less than values observed in previous studies at the HBEF. There was no relationship between frost depth, frost heaving and NO 3 -leaching, and a weak relationship between frost depth and winter N 2 O flux. There was a significant positive relationship between dissolved organic carbon (DOC) and NO 3 -concentrations in treatment plots but not in reference plots, suggesting that the snow manipulation treatment mobilized available C, which may have stimulated retention of N and prevented treatment effects on N losses. While the results support the hypothesis that climate change resulting in less snow and more soil freezing will increase N losses from northern hardwood forests, they also suggest that ecosystem response to soil freezing disturbance is affected by multiple factors that must be reconciled in future research.

Snow cover and soil moisture controls of freeze–thaw-related soil gas fluxes from a typical semi-arid grassland soil: a laboratory experiment

“…For example, most laboratory studies under controlled conditions did not include snow cover in their experimental designs, and soil moisture levels were usually adjusted before soil freezing (Priemé and Christensen 2001;Teepe et al 2004;Wu et al 2010a). However, snow cover has been reported to be particularly important for C and N trace gas fluxes during soil freezing and thawing (Groffman et al 2006(Groffman et al , 2011, since it can not only exert strong control on the dynamics of soil temperature and moisture (Buckeridge and Grogan 2010) but also significantly affect soil C and N turnover and soil microbial community structure and function (Feng et al 2007;Groffman et al 2011). Thus, the effects of snow cover and water from melting snow should be implemented in FTC studies.…”

The influence of soil frost on the quality of dissolved organic carbon in a boreal forest soil: combining field and laboratory experiments

“…Mortality of fine roots or lysis of freeze-damaged soil organisms (Soulides and Allison 1961), as well as an increased number of FTCs (Henry 2007) may also affect the soil DOC pool. To date, only a few field-scale studies have examined the effect of soil frost on DOC Fitzhugh et al 2001;Groffman et al 2001Groffman et al , 2010, and these have focused mainly on the release of DOC rather than its composition.…”

Impacts of Beech Bark Disease and Climate Change on American Beech

“…Much of the research of this nature is of great relevance to the future of American beech stands. For instance, some experimental studies have suggested that decreased snow cover in the winter (a result of increased winter temperatures) that leads to soil freezing may significantly alter the leaching of inorganic nitrogen and phosphorus in northern hardwood forests [53][54][55][56], in which American beech is frequently a component. However, there exists no clear, specific consensus in the scientific literature as to how soil ecosystems will respond to global climate change or how those changes will translate into specific changes in forest communities, insofar as we are aware.…”