M. Godde et al., CARBON MOBILIZATION FROM THE FOREST FLOOR UNDER RED SPRUCE IN THE NORTHEASTERN USA, Soil biology & biochemistry, 28(9), 1996, pp. 1181-1189
Global climate change may alter soil temperature and moisture conditio
ns, increasing the need to understand how these basic factors affect C
dynamics. This is particularly important in boreal forests, which oft
en have large C pools in the forest floor and mineral horizons. We exa
mined the effects of temperature and precipitation frequency on C dyna
mics in forest floor horizons from eight red spruce sites in the north
eastern U.S. using column leaching experiments. Intact and sieved fore
st floor samples were incubated at 3, 10 or 20 degrees C and leached e
ither daily, once per week, or twice per week during 14 to 39 days usi
ng simulated throughfall solutions (pH 2.7 or 4.0). Leachate DOC and C
O2 production were measured along with soil C and N concentrations. Fo
r intact samples, losses of C as DOC and as CO2 increased with increas
ing temperature, and the increase (Q(10)) was usually greater between
3 and 10 degrees C than between 10 and 20 degrees C. There was a great
er response of CO2 to temperature than of DOC (e.g. Howland sieved soi
l Q(10)s of 1.9 and 7.2 for CO2 and 1.5 and 2.0 for DOC at 3-10 and 10
-20 degrees C ranges, respectively). More frequent leaching increased
steady state DOC mobilization (e.g. 145 and 58 mu g g(-1) forest floor
d(-1) for daily and weekly leachings at 10 degrees C, respectively),
but not CO2 evolution (e.g. 79 and 74 mu g CO2-C g(-1) forest floor d(
-1) for daily and weekly leachings at 10 degrees C, respectively). Acr
oss the eight sites DOC loss and CO2 evolution varied by factors of 3.
6 and 4.0, respectively. Both CO2 evolution and DOC in leachates calcu
lated as fluxes were correlated (r = 0.73 and 0.87 respectively, n = 8
) with the C-to-N ratios of the samples (C-to-N ratios ranged from 27
to 58), which could be explained by N limitations that triggered selec
tive lignin degradation, differences in degree of humification of the
material, or position on a west-to-east pollution gradient. Although h
igher temperatures and more frequent leaching increased DOC mobilizati
on, and higher temperatures increased CO? evolution, both treatments a
nd site to site variation illustrate the complexity of the response of
forest-floor C pools to manipulations. Copyright (C) 1996 Elsevier Sc
ience Ltd