TY - JOUR
T1 - Effects of mild winter freezing on soil nitrogen and carbon dynamics in a northern hardwood forest
AU - Groffman, Peter M.
AU - Driscoll, Charles T.
AU - Fahey, Timothy J.
AU - Hardy, Janet P.
AU - Fitzhugh, Ross D.
AU - Tierney, Geraldine L.
N1 - Funding Information:
The authors thank Adam Welman and Jason Demers for excellent field, laboratory and data analysis work. We also thank Ann Gorham, Alan Lore-fice, Sibylle Otto and Dirk Koopmans for laboratory and data analysis support, Wayne Martin and Scott Nolan for help with site location and establishment and two anonymous reviewers for helpful comments. This research was supported by NSF Grant DEB-9652678, which was a product of the interagency program on Terrestrial Ecosystems and Global Change (TECO). This research was conducted at the Hubbard Brook Experimental Forest, which is owned and operated by the Northeastern Research Station, USDA Forest Service, Newtown Square, PA. This paper is a contribution to the Hubbard Brook Ecosystem Study.
PY - 2001
Y1 - 2001
N2 - 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-2y-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.
AB - 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-2y-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.
KW - Climate change
KW - Denitrification
KW - Microbial biomass
KW - Mineralization
KW - Nitrification
KW - Northern hardwood forest
KW - Soil freezing
UR - http://www.scopus.com/inward/record.url?scp=0035697813&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0035697813&partnerID=8YFLogxK
U2 - 10.1023/A:1013024603959
DO - 10.1023/A:1013024603959
M3 - Article
AN - SCOPUS:0035697813
VL - 56
SP - 191
EP - 213
JO - Biogeochemistry
JF - Biogeochemistry
SN - 0168-2563
IS - 2
ER -