Pd. Brooks et al., WINTER PRODUCTION OF CO2 AND N2O FROM ALPINE TUNDRA - ENVIRONMENTAL CONTROLS AND RELATIONSHIP TO INTER-SYSTEM C AND N FLUXES, Oecologia, 110(3), 1997, pp. 403-413
Fluxes of CO2 and N2O were measured from both natural and experimental
ly augmented snowpacks during the winters of 1993 and 1994 on Niwot Ri
dge in the Colorado Front Range. Consistent snow cover insulated the s
oil surface from extreme air temperatures and allowed heterotrophic ac
tivity to continue through much of the winter. In contrast, soil remai
ned frozen at sites with inconsistent snow cover and production did no
t begin until snowmelt. Fluxes were measured when soil temperatures un
der the snow ranged from -5 degrees C to 0 degrees C, but there was no
significant relationship between flux for either gas and temperature
within this range. While early developing snowpacks resulted in warmer
minimum soil temperatures allowing production to continue for most of
the winter, the highest CO2 fluxes were recorded at sites which exper
ienced a hard freeze before a consistent snowpack developed. Consequen
tly, the seasonal flux of CO2-C from snow covered soils was related bo
th to the severity of freeze and the duration of snow cover. Over-wint
er CO2-C loss ranged from 0.3 g C m(-2) season(-1) at sites characteri
zed by inconsistent snow cover to 25.7 g C m(-2) season(-1) at sites t
hat experienced a hard freeze followed by an extended period of snow c
over. In contrast to the pattern observed with C loss, a hard freeze e
arly in the winter did not result in greater N2O-N loss. Both mean dai
ly N2O fluxes and the total over-winter N2O-N loss were related to the
length of time soils were covered by a consistent snowpack. Over-wint
er N2O-N loss ranged from less 0.23 mg N m(-2) from the latest develop
ing, short duration snowpacks to 16.90 mg N m(-2) from sites with earl
y snow cover. These data suggest that over-winter heterotrophic activi
ty in snow-covered soil has the potential to mineralize from less than
1% to greater than 25% of the carbon fixed in ANPP, while over-winter
N2O fluxes range from less than half to an order of magnitude higher
than growing season fluxes. The variability in these fluxes suggests t
hat small changes in climate which affect the timing of seasonal snow
cover may have a large effect on C and N cycling in these environments
.