Forest floor carbon exchange of a boreal black spruce forest in eastern North America

Abstract

Abstract. This study reports continuous automated measurements of forest floor carbon (C) exchange over feathermoss, lichen, and sphagnum micro-sites in a black spruce forest in eastern North America during snow-free periods over three years. The response of soil respiration (R s-auto ) and forest floor photosynthesis (P ff ) to environmental factors was determined. The seasonal contributions of scaled up R s-auto adjusted for spatial representativeness (R s-adj ) and P ff (P ff -eco ) relative to that of total ecosystem respiration (R e ) and photosynthesis (P eco ), respectively, were also quantified.Shallow (5 cm) soil temperature explained 67-86% of the variation in R s-auto for all ground cover types, while deeper (50 and 100 cm) soil temperatures were related to R s-auto only for the feathermoss micro-sites. Base respiration was consistently lower under feathermoss, intermediate under sphagnum, and higher under lichen during all three years. The R s-adj /R e ratio increased from spring through autumn and ranged from 0.85 to 0.87 annually for the snow-free period. The R s-adj /R e ratio was negatively correlated with the difference between air and shallow soil temperature and this correlation was more pronounced in autumn than summer and spring.Maximum photosynthetic capacity of the forest floor (P ff max ) saturated at low irradiance levels (∼200 µmol m −2 s −1 ) and decreased with increasing air temperature and vapor pressure deficit for all three ground cover types, suggesting that P ff was more limited by desiccation than by light availability. P ff max was lowest for sphagnum, intermediate for feathermoss, and highest for lichen for two of the three years. P ff normalized for light Correspondence to: O. Bergeron (onil.bergeron@mcgill.ca) peaked at air temperatures of 5-8 • C, suggesting that this is the optimal temperature range for P ff . The P ff -eco /P eco ratio varied from 13 to 24% over the snow-free period and reached a minimum in mid-summer when both air temperature and P eco were at their maximum. On an annual basis, P ff -eco accounted for 17-18% of P eco depending on the year and the snow-free season totals of P ff -eco were 23-24% that of R s-adj .

Effect of measurement time of the day on the relationship between temperature and soil CO₂ efflux

“…Estimated cumulative seasonal (May to October) carbon effl ux from the forest soil based on continuous measurements was 6.3 t C ha −1 , which is comparable to other studies on spruce forests (Borken et al, 2002;Bergeron et al, 2009;GaumontGuay et al, 2009). There was no signifi cant diff erence (< 0.3 %) between seasonal fl ux calculated from measured CO 2 effl ux and CO 2 effl ux modeled using parameters calculated from the whole data set.…”

Surface CO2 Exchange Dynamics across a Climatic Gradient in McKenzie Valley: Effect of Landforms, Climate and Permafrost

“…Q 10 values for ER observed in the study (Tables 3 and 4) were within the range of values reported for boreal forest soils [56][57][58]. Many other studies on boreal forest stands [58,59] have shown that Ts (soil temperature) exerts a major influence on ER. Although, ER in uplands was primarily driven by soil temperature, high water table present in the collapse scar sites inhibited respiration [60].…”

“…Although temperature represented a significant control on the variability of the surface CO 2 fluxes in this study, other studies have found that water table depth or timing of the snowmelt play a more important role in predicting the CO 2 uptake capacity in many peatlands. For example, in a minerogenic peatland in Sweden, Peichl et al [58] found that the growing season NCE was strongly correlated with pre-growing season T air , (air temperature) and suggested that less root damage would occur during warmer winters and access to water by the vegetation would be easier. Similarly, in a mild maritime climate ombrotrophic bog, winter temperature would be a main control on the inter-annual variability in NEE [61].…”

The effect of atmospheric turbulence and chamber deployment period on autochamber CO&lt;sub&gt;2&lt;/sub&gt; and CH&lt;sub&gt;4&lt;/sub&gt; flux measurements in an ombrotrophic peatland

“…Wooden boardwalks were constructed to minimize disturbance during access to the chambers. The dynamic, closed autochamber system established at this bog was identical to the one used in a moderately rich treed fen , a temperate Douglas-fir forest (Drewitt et al, 2002), a boreal aspen forest (Griffis et al, 2004) and two boreal black spruce forests (Gaumont-Guay et al, 2008;Bergeron et al, 2009). The autochamber consisted of a transparent Plexiglas ® dome fitted to a PVC cylinder with a hinged aluminum frame.…”