Sf. Oberbauer et al., EFFECTS OF EXTENDED GROWING-SEASON AND SOIL WARMING ON CARBON-DIOXIDEAND METHANE EXCHANGE OF TUSSOCK TUNDRA IN ALASKA, J GEO RES-A, 103(D22), 1998, pp. 29075-29082
The active season of tussock tundra was extended during two growing se
asons (1995 and 1996) by snow removal in early season and prevention o
f snow accumulation in late season to test the effects of a longer gro
wing season on tundra carbon exchange. Three treatments were establish
ed: extended season, extended season + soil warming, and controls. Soi
l warming was accomplished using cold-frame, resistance heating wire i
nstalled the year prior to the initiation of treatments. Diurnal cours
es of CO2 exchange were measured weekly using infrared gas analysis wi
th enclosed chamber techniques. Methane fluxes were measured two to th
ree times a season also using enclosure methods. In 1995, snowmelt occ
urred unusually early, and snow removal treatments increased the seaso
n only 9-10 days. In 1996 the early season was increased approximately
24 days. As expected, thaw depth, soil temperature, and plant growth
were greater earlier in the extended season and extended season + soil
heating plots. Methane fluxes in both seasons were low but tended to
be higher in the extended season and soil heated plots. Net ecosystem
CO2 fluxes were similar among treatments early in the season, with a t
endency toward more positive fluxes (system loss) for the snow removal
and warmed plots, possibly due to higher belowground respiration. Dur
ing midseason, fluxes were similar among the treatments. Later in the
season, fluxes of extended season and warmed plots tended to be lower
(less carbon loss) than controls, especially in 1995. Totaled over the
season, however, the fluxes of the three treatments did not statistic
ally differ and represented losses to the atmosphere. Measurements of
dark respiration in 1996 indicate that both respiration and uptake wer
e increased on the extended season plots, resulting in similar net flu
xes to controls.