Annual ecosystem respiration budget for a <i>Pinus sylvestris</i> stand in central Siberia

Abstract

Using a ground-based and an above-canopy eddy covariance system in addition to stem respiration measurements, the annual respiratory fluxes attributable to soil, stems and foliage were determined for a Scots pine (Pinus sylvestris L.) forest growing in central Siberia. Night-time foliar respiration was estimated on the basis of the difference between fluxes measured below and above the canopy and the stem respiration measurements. Comparison of the effects of night-time turbulence on measured CO 2 fluxes showed flux loss above the canopy at low wind speeds, but no such effect was observed for the ground-based eddy system. This suggests that problems with flow homogeneity or flux divergence (both of which would be expected to be greater above the canopy than below) were responsible for above-canopy losses under these conditions. After correcting for this, a strong seasonality in foliar respiration was observed. This was not solely attributable to temperature variations, with intrinsic foliar respiratory capacities being much greater in spring and autumn. The opposite pattern was observed for stem respiration, with the intrinsic respiratory capacity being lower from autumn through early spring. Maximum respiratory activity was observed in early summer. This was not simply associated with a response to higher temperatures but seemed closely linked with cambial activity and the development of new xylem elements. Soil respiration rates exhibited an apparent high sensitivity to temperature, with seasonal data implying a Q 10 of about 7. We interpret this as reflecting covarying changes in soil microbial activity and soil temperatures throughout the snow-free season. Averaged over the two study years (1999 and 2000), the annual respiratory flux was estimated at 38.3 mol C m −2 a −1 . Of this 0.61 was attributable to soil respiration, with stem respiration accounting for 0.21 and foliar respiration 0.18.

Temperature Control of Spring CO2 Fluxes at a Coniferous Forest and a Peat Bog in Central Siberia

“…We determined the final day of snowmelt on which the 3-day moving average of Alb fell below 0.15 (15%) for the first time. To detect the final day of snowmelt, Shibistova et al [28] used the daily mean soil temperature at a depth of 0.05 m and a 15-day moving average as the final day of snowmelt; however, in the present study, we used diurnal patterns of surface or peat temperature at a depth of 0.04 (T s04 ). To examine the effect of temperature accumulation on vegetation productivity, we defined the accumulated growing degree days for air temperature (CGDD Ta ) and surface soil or peat temperature (CGDD Ts04 ).…”

“…At the beginning of snowmelt, the surface soil temperature exceeds 0 • C but remains close to 0 • C until snowmelt completion [21,25]. Once the snow has melted, surface soil temperature increases rapidly, and its diurnal cycle becomes pronounced [28]. Overall, the above mentioned studies demonstrate that the photosynthetic capacity of both boreal forests and peatlands are strongly influenced by the interannual variability in abiotic and environmental conditions during spring.…”

“…This lack of data motivated the first initiative of EC measurements in Siberia during 1999-2003 [15,38]. Various studies have quantified seasonal and inter-annual variabilities in CO 2 fluxes in Siberian boreal forests [15,28,36]. In addition, comparisons of CO 2 fluxes over the different peatland types have been reported [38][39][40].…”